Fix #264 and #262: Remove stale --resolve-collisions references

- Update examples/git-hooks README to use 'bd hooks install' instead of non-existent install.sh
- Fix post-merge hook error message to not suggest --resolve-collisions flag (removed in v0.20)
- Clean up all doc references to --resolve-collisions (flag removed, hash IDs prevent collisions)

Fixes #264 (git hooks installer missing)
Fixes #262 (misleading error message)

Amp-Thread-ID: https://ampcode.com/threads/T-c9f0e4cb-fba2-4db2-a3d5-36dc1892be9d
Co-authored-by: Amp <amp@ampcode.com>

docs/CLAUDE.md

@@ -44,7 +44,7 @@ Remote JSONL (shared across machines)
 
 - **Write path**: CLI → SQLite → JSONL export → git commit
 - **Read path**: git pull → JSONL import → SQLite → CLI
-- **Collision handling**: `bd import --resolve-collisions` (see AGENTS.md)
+- **Hash-based IDs**: Automatic collision prevention (v0.20+)
 
 Core implementation:
 - Export: `cmd/bd/export.go`, `cmd/bd/autoflush.go`