Runtime abstraction + browser REPL

Decouple ForthVM from wasmtime via a Runtime trait so the same outer
interpreter, compiler, and 200+ word definitions work on both native
(wasmtime) and browser (js-sys WebAssembly API) backends.

Runtime trait (runtime.rs):
- HostAccess trait for memory/global ops inside host function closures
- HostFn type: Box<dyn Fn(&mut dyn HostAccess) -> Result<()>>
- Runtime trait: memory, globals, table, instantiate, call, register

NativeRuntime (runtime_native.rs):
- Wraps wasmtime Engine/Store/Memory/Table/Global/Func
- CallerHostAccess bridges HostAccess to wasmtime Caller API
- Feature-gated behind "native" (default)

outer.rs refactor:
- ForthVM<R: Runtime> — generic over execution backend
- All 87 host functions converted from Func::new closures to HostFn
- All memory access via rt.mem_read/write_*, global access via rt.get/set_*
- Zero logic changes — pure API conversion

wafer-core feature gates:
- default = ["native"] includes wasmtime + all native modules
- Without "native": pure Rust only (outer, codegen, optimizer, dictionary)

Browser REPL (crates/web):
- WebRuntime: js-sys WebAssembly.Memory/Table/Global/Module/Instance
- WaferRepl: wasm-bindgen entry point (evaluate, data_stack, reset)
- WebAssembly.Function with Safari fallback (wrapper module)
- Frontend: dark terminal UI, word panel, init code editor, history
- Build: wasm-pack build --target web

All 452 tests pass (431 unit + 1 benchmark + 9 comparison + 11 compliance).

Cargo.lock

@@ -150,6 +150,12 @@ dependencies = [
  "allocator-api2",
 ]
 
+[[package]]
+name = "cast"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37b2a672a2cb129a2e41c10b1224bb368f9f37a2b16b612598138befd7b37eb5"
+
 [[package]]
 name = "cc"
 version = "1.2.58"
@@ -858,10 +864,12 @@ dependencies = [
 
 [[package]]
 name = "js-sys"
-version = "0.3.92"
+version = "0.3.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cc4c90f45aa2e6eacbe8645f77fdea542ac97a494bcd117a67df9ff4d611f995"
+checksum = "2964e92d1d9dc3364cae4d718d93f227e3abb088e747d92e0395bfdedf1c12ca"
 dependencies = [
+ "cfg-if",
+ "futures-util",
  "once_cell",
  "wasm-bindgen",
 ]
@@ -929,6 +937,16 @@ dependencies = [
  "rustix",
 ]
 
+[[package]]
+name = "minicov"
+version = "0.3.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4869b6a491569605d66d3952bcdf03df789e5b536e5f0cf7758a7f08a55ae24d"
+dependencies = [
+ "cc",
+ "walkdir",
+]
+
 [[package]]
 name = "nibble_vec"
 version = "0.1.0"
@@ -950,6 +968,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -957,6 +984,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
 dependencies = [
  "autocfg",
+ "libm",
 ]
 
 [[package]]
@@ -983,6 +1011,12 @@ version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
+[[package]]
+name = "oorandom"
+version = "11.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6790f58c7ff633d8771f42965289203411a5e5c68388703c06e14f24770b41e"
+
 [[package]]
 name = "petgraph"
 version = "0.6.5"
@@ -1298,6 +1332,15 @@ version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9774ba4a74de5f7b1c1451ed6cd5285a32eddb5cccb8cc655a4e50009e06477f"
 
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
 [[package]]
 name = "semver"
 version = "1.0.27"
@@ -1639,6 +1682,17 @@ dependencies = [
  "wasmtime",
 ]
 
+[[package]]
+name = "wafer-web"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "js-sys",
+ "wafer-core",
+ "wasm-bindgen",
+ "wasm-bindgen-test",
+]
+
 [[package]]
 name = "wait-timeout"
 version = "0.2.1"
@@ -1648,6 +1702,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "walkdir"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b"
+dependencies = [
+ "same-file",
+ "winapi-util",
+]
+
 [[package]]
 name = "wasi"
 version = "0.11.1+wasi-snapshot-preview1"
@@ -1674,9 +1738,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen"
-version = "0.2.115"
+version = "0.2.118"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6523d69017b7633e396a89c5efab138161ed5aafcbc8d3e5c5a42ae38f50495a"
+checksum = "0bf938a0bacb0469e83c1e148908bd7d5a6010354cf4fb73279b7447422e3a89"
 dependencies = [
  "cfg-if",
  "once_cell",
@@ -1686,10 +1750,20 @@ dependencies = [
 ]
 
 [[package]]
-name = "wasm-bindgen-macro"
-version = "0.2.115"
+name = "wasm-bindgen-futures"
+version = "0.4.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4e3a6c758eb2f701ed3d052ff5737f5bfe6614326ea7f3bbac7156192dc32e67"
+checksum = "f371d383f2fb139252e0bfac3b81b265689bf45b6874af544ffa4c975ac1ebf8"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eeff24f84126c0ec2db7a449f0c2ec963c6a49efe0698c4242929da037ca28ed"
 dependencies = [
  "quote",
  "wasm-bindgen-macro-support",
@@ -1697,9 +1771,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.115"
+version = "0.2.118"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "921de2737904886b52bcbb237301552d05969a6f9c40d261eb0533c8b055fedf"
+checksum = "9d08065faf983b2b80a79fd87d8254c409281cf7de75fc4b773019824196c904"
 dependencies = [
  "bumpalo",
  "proc-macro2",
@@ -1710,13 +1784,52 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.115"
+version = "0.2.118"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a93e946af942b58934c604527337bad9ae33ba1d5c6900bbb41c2c07c2364a93"
+checksum = "5fd04d9e306f1907bd13c6361b5c6bfc7b3b3c095ed3f8a9246390f8dbdee129"
 dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "wasm-bindgen-test"
+version = "0.3.68"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6bb55e2540ad1c56eec35fd63e2aea15f83b11ce487fd2de9ad11578dfc047ea"
+dependencies = [
+ "async-trait",
+ "cast",
+ "js-sys",
+ "libm",
+ "minicov",
+ "nu-ansi-term",
+ "num-traits",
+ "oorandom",
+ "serde",
+ "serde_json",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "wasm-bindgen-test-macro",
+ "wasm-bindgen-test-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-test-macro"
+version = "0.3.68"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "caf0ca1bd612b988616bac1ab34c4e4290ef18f7148a1d8b7f31c150080e9295"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "wasm-bindgen-test-shared"
+version = "0.2.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23cda5ecc67248c48d3e705d3e03e00af905769b78b9d2a1678b663b8b9d4472"
+
 [[package]]
 name = "wasm-compose"
 version = "0.245.1"