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.