feat!: unify mosaic CLI — native launcher, no bin/ directory

BREAKING CHANGE: ~/.config/mosaic/bin/ is removed entirely.
The mosaic npm CLI is now the only executable.

## What changed

- **bin/ → deleted**: All scripts moved to tools/_scripts/ (internal)
- **mosaic-launch → deleted**: Launcher logic is native TypeScript
  in packages/cli/src/commands/launch.ts
- **mosaic.ps1 → deleted**: PowerShell launcher removed
- **Framework install.sh**: Complete rewrite with migration system
- **Version tracking**: .framework-version file (schema v2)
- **Migration v1→v2**: Auto-removes bin/, cleans old PATH entries
  from shell profiles

## Native TypeScript launcher (commands/launch.ts)

All runtime launch logic ported from bash:
- Runtime prompt builder (AGENTS.md + RUNTIME.md + USER.md + TOOLS.md)
- Mission context injection (reads .mosaic/orchestrator/mission.json)
- PRD status injection (scans docs/PRD.md)
- Pre-flight checks (MOSAIC_HOME, AGENTS.md, SOUL.md, runtime binary)
- Session lock management with signal cleanup
- Per-runtime launch: Claude, Codex, OpenCode, Pi
- Yolo mode flags per runtime
- Pi skill discovery + extension loading
- Framework management (init, doctor, sync, bootstrap) delegates
  to tools/_scripts/ bash implementations

## Installer

- tools/install.sh: detects framework by .framework-version or AGENTS.md
- Framework install.sh: migration system with schema versioning
- Forward-compatible: add migrations as numbered blocks
- No PATH manipulation for framework (npm bin is the only PATH entry)

scripts/agent/orchestrator-daemon.sh

@@ -69,12 +69,12 @@ case "$cmd" in
       echo "[agent-framework] orchestrator already running (pid=$(cat "$PID_FILE"))"
       exit 0
     fi
-    nohup "$MOSAIC_HOME/bin/mosaic-orchestrator-drain" --poll-sec "$poll_sec" $sync_arg >"$LOG_FILE" 2>&1 &
+    nohup "$MOSAIC_HOME/tools/_scripts/mosaic-orchestrator-drain" --poll-sec "$poll_sec" $sync_arg >"$LOG_FILE" 2>&1 &
     echo "$!" > "$PID_FILE"
     echo "[agent-framework] orchestrator started (pid=$!, log=$LOG_FILE)"
     ;;
   drain)
-    exec "$MOSAIC_HOME/bin/mosaic-orchestrator-drain" --poll-sec "$poll_sec" $sync_arg
+    exec "$MOSAIC_HOME/tools/_scripts/mosaic-orchestrator-drain" --poll-sec "$poll_sec" $sync_arg
     ;;
   stop)
     if ! is_running; then