Replace implicit note shorthand with explicit addnote command and split README

Two changes:

1. structured-add-commands: The implicit note shorthand (kb "text") caused
   accidental note creation from mistyped commands. Replaced with explicit
   kb addnote <text> command. Root command reverts to standard Cobra
   behaviour. Updated examples, tests, SKILL.md, and specs.

2. split-readme-developer-docs: Moved build-from-source instructions, release
   process, API reference, and ROCm migration notes from README.md into a
   new DEVELOPER.md. README now links to DEVELOPER.md for dev workflows.

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

DEVELOPER.md

@@ -0,0 +1,100 @@
+# Developer Guide
+
+Instructions for building from source, releasing, and contributing to kb.
+
+## Building from source
+
+### Engine
+
+```bash
+cd engine
+
+# NVIDIA GPU
+KB_DATA_PATH=~/kb-data docker compose -f compose.nvidia.yaml up -d
+
+# AMD GPU (ROCm)
+KB_DATA_PATH=~/kb-data docker compose -f compose.rocm.yaml up -d
+```
+
+### Client
+
+```bash
+cd client
+make build    # produces ./kb binary
+make all      # or cross-compile: dist/kb-{os}-{arch}
+```
+
+## Building and releasing
+
+Client and engine are versioned independently via `client/VERSION` and `engine/VERSION`. Each has its own release script and git tag prefix.
+
+### Release client
+
+```bash
+./release-client.sh --gitea              # patch bump, release via Gitea
+./release-client.sh --github --minor     # minor bump, release via GitHub
+./release-client.sh --gitea --no-increment  # release current version as-is
+./release-client.sh --gitea --dry-run    # preview without doing anything
+```
+
+Creates tag `client-vX.Y.Z`, builds Go binaries for all platforms, and creates a Gitea/GitHub release with binaries attached.
+
+The client embeds a `MinEngineVersion` (from `client/MIN_ENGINE_VERSION`) and will hard-fail if the connected engine is too old.
+
+### Release engine
+
+```bash
+./release-engine.sh --gitea              # patch bump, release via Gitea
+./release-engine.sh --github --minor     # minor bump, release via GitHub
+./release-engine.sh --gitea --no-increment  # release current version as-is
+./release-engine.sh --gitea --dry-run    # preview without doing anything
+```
+
+Creates tag `engine-vX.Y.Z`, builds NVIDIA and ROCm Docker images, creates a Gitea/GitHub release, and pushes images to the registry.
+
+### Checking versions
+
+```bash
+# Client
+kb --version
+
+# Engine
+curl http://localhost:8000/api/v1/status | jq .version
+```
+
+### Docker images
+
+Images are pushed to `docker.dcglab.co.uk/dcg/kb/engine` with tags:
+
+- `engine-v2.0.6-nvidia` / `engine-v2.0.6-rocm` — versioned
+- `latest-nvidia` / `latest-rocm` — latest release
+
+Override the registry and org via environment variables:
+
+```bash
+REGISTRY=ghcr.io IMAGE_ORG=myorg ./release-engine.sh --github
+```
+
+## API reference
+
+All endpoints are under `/api/v1/`. Requires `Authorization: Bearer <key>` header when `KB_API_KEY` is set.
+
+| Method | Endpoint | Description |
+|---|---|---|
+| `GET` | `/health` | Health check (bypasses auth) |
+| `POST` | `/search` | Hybrid search (JSON body) |
+| `POST` | `/jobs` | Upload file/note for ingestion (multipart, returns 202 or 409 if duplicate) |
+| `GET` | `/jobs` | List ingestion jobs |
+| `GET` | `/jobs/{id}` | Job details |
+| `GET` | `/documents` | List documents |
+| `GET` | `/documents/{id}` | Document details with chunks |
+| `GET` | `/documents/{id}/file` | Download original file |
+| `DELETE` | `/documents/{id}` | Remove a document (and stored file) |
+| `PUT` | `/documents/{id}/tags` | Add/remove tags |
+| `GET` | `/tags` | List all tags |
+| `GET` | `/status` | Engine status, GPU info, DB stats |
+| `POST` | `/reindex` | Re-embed all chunks |
+
+## Future: ROCm runtime migration
+
+The `onnxruntime-rocm` execution provider was removed from onnxruntime as of v1.23. AMD is pushing toward the **MIGraphX execution provider** as the replacement for ROCm GPU inference. When upgrading onnxruntime beyond v1.22, the ROCm Dockerfile will need to switch from `onnxruntime-rocm` to `onnxruntime` with the MIGraphX EP and install the `migraphx` runtime libraries instead.