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>

examples/claude-code-skill/references/CLI_REFERENCE.md

@@ -48,7 +48,7 @@ Complete command reference for bd (beads) CLI tool. All commands support `--json
 | `bd stats` | Get project statistics | `--json` |
 | `bd blocked` | Find blocked issues | `--json` |
 | `bd export` | Export issues to JSONL | `--json` |
-| `bd import` | Import issues from JSONL | `--resolve-collisions` |
+| `bd import` | Import issues from JSONL | `--dedupe-after`, `--dry-run` |
 | `bd init` | Initialize bd in directory | `--prefix` |
 | `bd quickstart` | Show quick start guide | (no flags) |