docs: add contributor docs, community infrastructure, and roadmap rewrite

- Add root CONTRIBUTING.md with incentives (paper acknowledgment, Mac Mini
  giveaway), contribution tiers, PR process, and maintainership path
- Add CODE_OF_CONDUCT.md (Contributor Covenant v2.1)
- Add .pre-commit-config.yaml with ruff lint + format hooks
- Add GitHub issue templates (bug report, feature request, new eval dataset)
- Add PR template with test/lint/format checklist
- Rewrite docs roadmap with GitHub Projects structure, current focus areas,
  and collapsible version history
- Remove Development section from MkDocs nav; replace with top-level Roadmap tab
- Delete changelog, extending docs (consolidated into CONTRIBUTING.md)
- Delete root ROADMAP.md (content now lives in docs site)
- Add pre-commit to dev extras in pyproject.toml
- Add Roadmap link to README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/pull_request_template.md

@@ -0,0 +1,16 @@
+## What does this PR do?
+
+<!-- Brief description of the change and its motivation -->
+
+## How was this tested?
+
+<!-- Describe tests added or manual testing performed -->
+
+## Checklist
+
+- [ ] Tests pass (`uv run pytest tests/ -v`)
+- [ ] Linter passes (`uv run ruff check src/ tests/`)
+- [ ] Formatter passes (`uv run ruff format --check src/ tests/`)
+- [ ] New/changed public API has docstrings
+- [ ] Follows registry pattern (if adding new component)
+- [ ] Documentation updated (if applicable)