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)

packages/mosaic/framework/tools/orchestrator/session-run.sh

@@ -80,11 +80,11 @@ echo -e "${C_CYAN}Capsule:${C_RESET} $(next_task_capsule_path "$PROJECT")"
 
 cd "$PROJECT"
 if [[ "$YOLO" == true ]]; then
-  exec "$MOSAIC_HOME/bin/mosaic" yolo "$runtime" "$launch_prompt"
+  exec mosaic yolo "$runtime" "$launch_prompt"
 elif [[ "$runtime" == "claude" ]]; then
-  exec "$MOSAIC_HOME/bin/mosaic" claude "$launch_prompt"
+  exec mosaic claude "$launch_prompt"
 elif [[ "$runtime" == "codex" ]]; then
-  exec "$MOSAIC_HOME/bin/mosaic" codex "$launch_prompt"
+  exec mosaic codex "$launch_prompt"
 fi
 
 echo -e "${C_RED}Unsupported coord runtime: $runtime${C_RESET}" >&2