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>

openspec/changes/archive/2026-03-31-split-readme-developer-docs/tasks.md

@@ -0,0 +1,17 @@
+## 1. Create DEVELOPER.md
+
+- [x] 1.1 Create DEVELOPER.md at repo root with engine build-from-source instructions (compose.nvidia.yaml and compose.rocm.yaml)
+- [x] 1.2 Add client build-from-source instructions (make build, make all)
+- [x] 1.3 Add "Building and releasing" section: release-client.sh and release-engine.sh usage with all flag options
+- [x] 1.4 Add version checking instructions (kb --version, curl status endpoint)
+- [x] 1.5 Add Docker image tag conventions and registry override documentation
+- [x] 1.6 Add "Future: ROCm runtime migration" developer note
+
+## 2. Trim README.md
+
+- [x] 2.1 Remove "From source (for development)" subsection under engine quick start
+- [x] 2.2 Remove "From source (for development)" subsection under client installation
+- [x] 2.3 Remove entire "Building and releasing" section
+- [x] 2.4 Remove "Future: ROCm runtime migration" section
+- [x] 2.5 Add cross-reference note to DEVELOPER.md in the Quick Start section for building from source
+- [x] 2.6 Move API reference section from README.md to DEVELOPER.md