Reindex command, implicit note shorthand, add→addfile rename

- Add `kb reindex` command with confirmation prompt and --yes flag
- Add implicit note shorthand: `kb "my note"` submits a note directly
- Rename `add` to `addfile`, remove --note/--title/--type flags
- Add client-side file extension validation before upload
- Add `kb examples` command for common usage patterns
- Update README, SKILL.md, and main specs
- Archive completed changes and sync delta specs

BREAKING: `kb add` renamed to `kb addfile`, `kb add --note` replaced by `kb "text"`

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/archive/2026-03-29-client-reindex-command/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-29