feat(plugin): write-path trigger — offer prior art before code is rewritten

The milestone headline. Auto-inject fires on the operator's prompt; the
moment reuse is actually lost is later, when the agent decides mid-task to
write a helper. A PreToolUse hook on Write|Edit now fires there.

Channel: `additionalContext` with NO permissionDecision, so the note reaches
Claude beside the tool result and the write is never blocked — a recall aid
must not be able to stop the operator's work. Plain stdout would have been
invisible to the model, and deny/ask would have made a nudge into a gate.

Two arms, different in kind:
- BY PLACE — a snippet recorded at this path (or its directory) is prior art
  by definition, not resemblance, so it is neither scored nor thresholded.
  This is what #2083's reverse lookup was built to answer.
- BY MEANING — semantic search restricted to snippets (new `note_type` filter
  on semantic_search_notes) over the code about to be written.
Place ranks first; the top-k cap spans both arms.

Gates carried over from milestone 93 verbatim: threshold, margin, session
dedup, titles-never-bodies. Own `source='write_path'` in retrieval_logs so
precision is tunable separately — the docstring records that the place arm
is unlogged and hands that to #2085.

Its own on/off in Settings but the SAME threshold/top-k: one "how loud may
Scribe be" knob is easier to reason about than two that drift, and splitting
them later is then a data-backed change rather than a guess.

Details worth keeping: the hook sends a REPO-RELATIVE path because that is
how locations are recorded; the git remote resolves to a project and is never
used as the location `repo` filter (different namespaces, would silently
match nothing); the endpoint stays a GET because a read-scoped API key cannot
POST and every other hook depends on that.

plugin.json 0.1.17 -> 0.1.18. Refs #2082, milestone #232.

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
   "description": "Scribe system-of-record for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming, reusing-code), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.17",
+  "version": "0.1.18",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {