Add setup-matt-pocock-skills; rename github-triage to triage; migrate engineering skills to vague prose

Engineering skills no longer hard-code GitHub or specific label strings.
A new setup skill scaffolds an `## Agent skills` block in
AGENTS.md/CLAUDE.md plus `docs/agents/` so each repo can declare its own
backlog backend, triage label vocabulary, and domain doc layout. Skills
that need the mapping (to-issues, to-prd, triage) point at the setup
skill; skills that only soften with it (diagnose, tdd,
improve-codebase-architecture, zoom-out) stay vague. ADR-0001 records
the split.

Closes #88, #89.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/adr/0001-explicit-setup-pointer-only-for-hard-dependencies.md

@@ -0,0 +1,10 @@
+# Explicit `/setup-matt-pocock-skills` pointer only for hard dependencies
+
+Engineering skills depend on per-repo config (backlog backend, triage label vocabulary, domain doc layout) seeded by `/setup-matt-pocock-skills`. Some skills cannot meaningfully function without that config — they have to publish to a specific backlog or apply a specific label string. Others only use it to sharpen output (vocabulary, ADR awareness) and degrade gracefully without it.
+
+We split these into **hard-dependency** and **soft-dependency** skills:
+
+- **Hard dependency** (`to-issues`, `to-prd`, `triage`) — include an explicit one-liner: _"… should have been provided to you — run `/setup-matt-pocock-skills` if not."_ Without the mapping, output is wrong, not just fuzzy.
+- **Soft dependency** (`diagnose`, `tdd`, `improve-codebase-architecture`, `zoom-out`) — reference "the project's domain glossary" and "ADRs in the area you're touching" in vague prose only. If the docs aren't there, the skill still works; output is just less sharp.
+
+The split keeps soft-dependency skills token-light and avoids cargo-culting the setup pointer into places where it isn't load-bearing.