Backend: `links::resolve_id` now checks for an exact live node id before
alias/title, so a canonical `[[NODEID]]` link resolves to its node and
can't be shadowed by a like-named node. Legacy `[[Name]]` links still
resolve by name (until the migration), so this is additive.
heph.nvim: `link.insert` (bound to insert-mode `[[` and `:Heph link`)
searches via the `search` RPC and inserts `[[NODEID]]`, with a "+ Create
new doc" entry; `<CR>` follow resolves the id directly. e2e covers
search→insert→materialize and the create path.
Remaining (§8.4): read-expansion/conceal display + the one-time
[[Title]]→[[NODEID]] migration (then retire name-resolution + the hack).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
