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/specs/docker-deployment/spec.md

@@ -67,7 +67,7 @@ The engine SHALL store all persistent state (SQLite database, HF model cache, st
 
 ### Requirement: Compose files for deployment
 
-The project SHALL provide Docker Compose files for single-command deployment.
+The project SHALL provide Docker Compose files for single-command deployment. Compose files SHALL use `build:` context for local development. Release notes SHALL document the versioned image tag for users pulling pre-built images.
 
 #### Scenario: Start NVIDIA deployment
 - **WHEN** an admin runs `docker compose -f compose.nvidia.yaml up -d`
@@ -85,6 +85,10 @@ The project SHALL provide Docker Compose files for single-command deployment.
 - **WHEN** an admin sets environment variables in the compose file (KB_MODEL, KB_API_KEY, KB_DEVICE, etc.)
 - **THEN** the engine SHALL use those values
 
+#### Scenario: Pre-built image deployment
+- **WHEN** an admin wants to use a pre-built engine image without building from source
+- **THEN** the engine release notes SHALL include the exact `docker pull` command with the versioned tag (e.g. `docker.dcglab.co.uk/dcg/kb/engine:engine-v2.1.0-nvidia`)
+
 ---
 
 ### Requirement: CPU-only fallback