docs: 📝 openspec proposal for MCP resource templates
Add full OpenSpec change `mcp-resource-templates` covering the design
for exposing core Forgejo entities as URI-addressable MCP resources:
owner, repo, commit, issue, pr, comment, and commit-status.
Artifacts:
- proposal.md: why + capability list for all 7 entities
- design.md: 13 decisions (URI scheme, coexist-vs-replace, bounding,
caching, auth, rollout order, client compat matrix)
- specs/: 8 spec files with ADDED Requirements + Scenario blocks
- tasks.md: 7 slices (core framework → entity-by-entity → docs)
Driven by forgejo-mcp-1l5. Implementation via /opsx:apply.