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/feature_request.md

@@ -0,0 +1,26 @@
+---
+name: Feature request
+about: Suggest an idea or improvement
+title: "[Feature] "
+labels: ["enhancement"]
+---
+
+<!-- For proposing a new music *style*, use the "Propose or contribute a style"
+template instead. -->
+
+## The problem / the jam moment
+
+<!-- What are you trying to do, and where does the app fall short today? -->
+
+## What you'd like to see
+
+
+
+## How it fits the roadmap
+
+<!-- Optional: does this relate to something in GOAL.md (detection, the Jam Guide,
+the Progression Builder, the Learn drills)? -->
+
+## Alternatives or references
+
+<!-- Other tools that do this well, or workarounds you've tried. -->