feat: Notion backend for the catalog + set command + ls/source/save UX

Persist the entry catalog to a Notion page instead of an external script.

- `hel store notion:<ref>` reads the dump from stdin and writes it into a
  single code block on the page; `hel load notion:<ref>` prints it back.
  `<ref>` is a page id (UUID) or a page title (case-insensitive search).
  Token from HEL_NOTION_TOKEN. Networking lives in helcli (ureq + serde_json);
  the core lib and the wasm build are untouched. argv is dispatched before the
  REPL starts, so the subcommands never read ~/.helrc or prompt for a master.

- `set <key> <value>`: runtime config (e.g. hel_dump, hel_notion_token) from
  ~/.helrc instead of env vars. The map is exported (uppercased) into spawned
  pipe/source children, so `set hel_notion_token ...` reaches `hel store`.
  Values are redacted in history.

- `ls` now matches case-insensitively.
- `source` echoes `source <target>`.
- `save` prints a `< removed` / `> added` diff against the last load/save
  snapshot so removals are noticed before they persist.

hel/src/parser.rs

@@ -9,7 +9,7 @@ peg::parser! {
         pub rule cmd() -> Command<'input> = c:(info_cmd_list() / mod_cmd_list() / enc_cmd_list() / asides_cmd_list()) { c }
         pub rule info_cmd_list() -> Command<'input> = space()* c:(ls_cmd() / ld_cmd() / pb_cmd() / save_cmd() / save_def_cmd() / dump_cmd()) { c }
         pub rule mod_cmd_list() -> Command<'input> = space()* c:(add_cmd() / keep_cmd() / mv_cmd() / rm_cmd() / comment_cmd ()) { c }
-        pub rule asides_cmd_list() -> Command<'input> = space()* c:(help_cmd() / source_cmd() / quit_cmd() / noop_cmd() / error_cmd()) { c }
+        pub rule asides_cmd_list() -> Command<'input> = space()* c:(help_cmd() / source_cmd() / set_cmd() / quit_cmd() / noop_cmd() / error_cmd()) { c }
         pub rule enc_cmd_list() -> Command<'input> = space()* c:(enc_cmd() / gen_cmd() / pass_cmd() / unpass_cmd() / correct_cmd() / uncorrect_cmd()) { c }
         pub rule script() -> Vec<Command<'input>> = c:(info_cmd_list() / mod_cmd_list() / enc_cmd_list() / asides_cmd_list()) ++ "\n" { c }
 
@@ -86,6 +86,7 @@ peg::parser! {
         rule save_def_cmd() -> Command<'input> = "save" { Command::Dump(None) }
         rule dump_cmd() -> Command<'input> = "dump" { Command::Dump(Some("-".to_string())) }
         rule source_cmd() -> Command<'input> = "source" _ s:$(([' '..='~'])+) { Command::Source(s.to_string()) }
+        rule set_cmd() -> Command<'input> = "set" _ k:word() _ v:$(([' '..='~'])+) { Command::Set(k, v.to_string()) }
         rule ls_cmd() -> Command<'input> = "ls" f:comment()? { Command::Ls(f.unwrap_or(".".to_string())) }
         rule ld_cmd() -> Command<'input> = "ld" f:comment()? { Command::Ld(f.unwrap_or(".".to_string())) }
         rule add_cmd() -> Command<'input> = "add" _ name:name() { Command::Add(Password::from_password(name)) }