feat(model-router): wave 3-B — first-use dialog with context, model then effort on change

The dialog now explains what it asks about: the skill's description (from
its SKILL.md frontmatter, five YAML forms, first sentence, cleaned), the
agent's description (from agent.offer), the phase's new 'about' line in
routing.json, and the real model id and effort the next step runs on.
Options Later / Keep / Change; Change asks the model (fable, opus, sonnet,
haiku with their tier role), then the effort among those the phases of
that model offer, then the scope; the pair maps to an existing phase (rows
stay phase names; the row's current phase wins a tie; same phase = Keep).
A main-loop phase (T3) is Later / Keep only. A main-row change toasts the
real decision and the /route switch hint when the pick is a downgrade.
Descriptions pass a hardened read (name allowlist, stat kind, size cap)
and clean(). Kit suite 190 → 232; W3-A dialog tests migrated.

Contract .claude/tasks/contracts/2026-10-11-model-router-w3b-dialog-1240.md,
plan r3: 3 lenses (2 BLOCKERs: inline rows, phase edits) + 1 confirmation,
feater + 2 rounds, GATE 0 MET, verifier CONFORME (3rd pass), security PASS.

lib/effort-shift.md

@@ -48,8 +48,8 @@ Builtin `/effort` is NOT a lever inside a run: rows and routes outrank it.
   typed marker (unverified live 2026-10-10).
 - Headless (`-p`, SDK) runs the hooks, so routing works there too.
 - Mod off: typed agents fall back to their `model:`/`effort:` frontmatter.
-- First use of a row asks once (Keep, Later or another phase, then
-  Everywhere or this project only); the answer is kept in
+- First use of a row asks once, with context (Later, Keep or Change: model,
+  then effort, then Everywhere or this project only); the answer is kept in
   `mods/model-router/routing.json`. `/route pending` lists what is still
   unconfirmed, `/route ask off|on` toggles the dialog.