docs: CONTRIBUTING.md + issue templates — the musician contribution path (task H-02)

'Add a style without deep coding' centerpiece: KB data contract, mirror gospel pack,
register, run validator; explains why the validator exists; /kb-expand assisted path;
PR checklist. add-style/bug_report/feature_request templates + config.yml. License flagged
unsettled, not decided. Critic PASS (all links/commands verified, schema-faithful).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/add-style.md

@@ -0,0 +1,46 @@
+---
+name: Propose or contribute a style
+about: Suggest a genre for the knowledgebase, or offer to author one
+title: "[Style] "
+labels: ["style", "content"]
+---
+
+<!--
+Style packs are data, not code — see CONTRIBUTING.md ("Add a music style without
+deep coding") and src/data/kb/SCHEMA.md. You can propose a style for someone else
+to build, or claim it yourself.
+-->
+
+## Which style / genre?
+
+<!-- e.g. Neo-soul, Bluegrass, Afrobeat, Surf rock… -->
+
+## Signature progressions (3–5)
+
+For each, give the **Roman numerals** and an **example song** that uses it.
+
+<!--
+Example:
+1. ii–V–I  (e.g. "Misty")
+2. I–vi–ii–V  (1950s turnaround, e.g. "Stand By Me")
+3. i7–IV7 Dorian vamp  (e.g. "Chameleon")
+-->
+
+1.
+2.
+3.
+
+## What makes it sound like itself?
+
+<!-- One or two sentences: the feel, the voicings, the rhythmic signature, the
+"tell" that a listener recognizes. -->
+
+## Will you author the voicings, or want help?
+
+- [ ] I'll author the pack myself (guitar voicings / comping / improv) and open a PR
+- [ ] I can supply the progressions and theory, but want help turning them into the data files
+- [ ] I'm proposing the style for someone else to build
+
+## Anything else?
+
+<!-- Instrument focus (guitar/piano/bass), sources, reference recordings, etc. -->