feat: implement T01-T04 — Go module, canonical model, LDAP validator, error taxonomy

- T01: Go module (keycape), full directory skeleton, Makefile, CI workflow
- T02: spec/canonical-model.yaml with 6 entities + Go domain types
- T03: spec/ldap-schema.yaml + validator binary with structural/semantic rules
- T04: Error taxonomy — 4 stable error types, JSON format, HTTP helpers

28 tests pass, go vet clean, go build clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/ralph-loop.local.md

@@ -0,0 +1,33 @@
+---
+active: true
+iteration: 1
+session_id: 
+max_iterations: 30
+completion_promise: "HEUREKA"
+started_at: "2026-03-13T00:07:01Z"
+---
+
+Do a high quality implementation of workplan KEY-WP-0001-keycape-implementation.md as follows:
+
+Requirements and Boundaries
+- Keep the scope of the workplan
+- Use documents in spec/ and wiki/ folder to understand the big picture
+- Document important architecture decisions as ADRs in the architecture/ folder
+- Save relevant parts of documentation you need to grab online to the research/ folder
+- Keep the state-hub up to date with task completions
+- If stuck and when running out of iterations document what went wrong in problems/ folder
+
+WHILE TDD-Loop for all tasks:
+1) RED: write test → run → fail
+2) GREEN:  implement minimal code → run → pass
+3) REFACTOR: refactor → run → pass
+REPEAT
+
+Success Criteria:
+- No linter errors
+- All tasks and requirements of workplan implemented
+- Documentation updated showing how the application works
+- Check Workstream DoD from the state-hub policies
+
+Refine until all succes-criteria have been met, otherwise 
+output <promise>HEUREKA</promise> when done!