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>

internal/tasks/marvin.go

@@ -31,7 +31,8 @@ func execRunner(ctx context.Context, name string, args ...string) ([]byte, error
 // (`am --json`, no subcommand) and parses the open tasks due today or earlier.
 type Marvin struct {
 	cmd  string
-	args []string
+	base []string // configured prefix after cmd, without the "--json" sentinel
+	args []string // read-path argv: base + ["--json"]
 	run  runner
 }
 
@@ -43,9 +44,9 @@ func NewMarvin(command string) *Marvin {
 	if len(fields) == 0 {
 		fields = []string{"am"}
 	}
-	args := append([]string{}, fields[1:]...)
-	args = append(args, "--json")
-	return &Marvin{cmd: fields[0], args: args, run: execRunner}
+	base := append([]string{}, fields[1:]...)
+	args := append(append([]string{}, base...), "--json")
+	return &Marvin{cmd: fields[0], base: base, args: args, run: execRunner}
 }
 
 // Today returns the open tasks due today or earlier, or an error if the CLI
@@ -58,6 +59,16 @@ func (m *Marvin) Today(ctx context.Context) ([]Task, error) {
 	return parse(out)
 }
 
+// Create adds a new task via ampy's `add` subcommand, shelling out through the
+// same configured prefix as the read path so the add lands in the same CRDT
+// store the reads observe. Only the title is sent in v1. It returns the CLI
+// error on failure.
+func (m *Marvin) Create(ctx context.Context, t Task) error {
+	args := append(append([]string{}, m.base...), "add", t.Title, "--json")
+	_, err := m.run(ctx, m.cmd, args...)
+	return err
+}
+
 type rawTask struct {
 	ID    string `json:"id"`
 	Title string `json:"title"`