feat(model-router): wave 4-B — prompt classifier

Plain composer prompts with no route in force get a turn-scoped effort
from $.model.classify (design/analysis/coding/bookkeeping/chat → phase
effort, effort only, never the model). Bounded by a 3 s clock race, a
user interrupt neither counts nor writes, three failures in a row pause
it for cooldownMinutes (one toast, status marker, cleared by /route
reload). No dialog, no routing.json write on a classified route. New
Config key `classify` (default on, pickSwitch), `/route classify on|off`
session toggle, `/route show` line and argumentHint. An explicit user
/effort beats the guess (engineBase check).

Docs: README classifier paragraph, USAGE row + sentence, CHANGELOG,
effort-shift.md. Kit suite 428 tests.

lib/effort-shift.md

@@ -47,6 +47,8 @@ Builtin `/effort` is NOT a lever inside a run: rows and routes outrank it.
 - A skill typed while a background agent is live routes only through the
   typed marker (unverified live 2026-10-10).
 - Headless (`-p`, SDK) runs the hooks, so routing works there too.
+- A plain typed prompt with no route in force gets its turn effort from a
+  small-model classifier (effort only; `/route classify off`; never `-p`).
 - Mod off: typed agents fall back to their `model:`/`effort:` frontmatter.
 - 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