Generalize the focus controller into a harness hosting swappable modes

Loosen AntiDrift's session controller into Keel's general collect→brain→act
loop. A new internal/harness runs at most one mode.Mode at a time, fanning
async completions out to the web SSE and status-bar surfaces.

- internal/mode: the Mode contract (Kind/Command/View/Active) plus optional
  EvidenceConsumer and Expirer ports, and the surfacing Envelope.
- internal/mode/focus: the former session/domain/statemachine packages moved
  under the mode, now satisfying the harness contracts unchanged.
- internal/mode/offscreen: a one-shot away-from-desk mode built on the new
  ai.Proposer, which turns a life-domain brief into one off-screen action.
- cmd/keeld replaces cmd/antidriftd; daemon wires focus + offscreen factories
  with per-mode persistence under ~/.keel/modes/<kind>.
- Finish the rename: KEEL_* env refs in the README, /keeld build artifact
  ignored, stale antidriftd binary removed.

Include the design + implementation plan this refactor was built from under
docs/superpowers/{specs,plans}/2026-06-04-controller-refactor*.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

AGENTS.md

@@ -17,7 +17,7 @@ acts on the reply.
   DB / event store. Buckets hold *pointers*, not copies.
 - **Frame** — `~/owc` (values, goals, `resources/bug-*.md` life-bugs). Reference,
   never duplicate.
-- **Surfaces** — a phone-friendly web UI + the WM status bar (`~/.antidrift_status`).
+- **Surfaces** — a phone-friendly web UI + the WM status bar (`~/.keel_status`).
 - **Effectors** — gated writes (Marvin tasks, capture, AntiDrift enforce; later
   Beeminder datapoints, `~/owc` notes). Start propose-and-confirm; trend toward
   autonomy. The gate is per-effector config — Felix's agency-vs-cage dial.
@@ -31,17 +31,16 @@ acts on the reply.
 general *collect → brain → act* loop where a focus-session is one mode among many.
 
 ```bash
-go run ./cmd/antidriftd   # local web UI at http://localhost:7777
+go run ./cmd/keeld   # local web UI at http://localhost:7777
 go test ./...
 ```
 
 ## Naming / rename status
 
-The directory and git repo are **`keel`**. The **code identity is intentionally
-still `antidrift`** — Go module `antidrift`, `antidriftd` binary, `~/.antidrift/`
-runtime, `ANTIDRIFT_*` env. The code rename lands later, *with a state migration*
-(`~/.antidrift/` owns the live ledger), during the controller refactor. Don't
-`mv ~/.antidrift` or rename the module casually.
+The rename is **complete**. Directory, git repo, Go module, binary, runtime, and
+env are all `keel`: module `keel`, binary `keeld`, runtime `~/.keel/`,
+`KEEL_*` env. If you have a live ledger under the old `~/.antidrift/` directory,
+move it manually to `~/.keel/` — there is no automated migration tool.
 
 ## How to work here