Improve build workflow with version bump selection and changelog in releases (#104)

## Summary

- Add `version_type` choice input with options: BUMP_PATCH (default), BUMP_MINOR, BUMP_MAJOR, SPECIFIC_VERSION
- Add optional `specific_version` input for explicit version selection
- Include changelog content in Forgejo release body under "What's Changed" section
- Move CHANGELOG.md to repository root (still copied into docs during Quartz build)
- Add CHANGELOG link to docs index page
- Update doc-links script to recognize build-time docs from repo root

## Changes

**Workflow inputs:**
- Previously: single optional `version` string input
- Now: `version_type` choice dropdown (defaults to BUMP_PATCH) + optional `specific_version` for explicit versions

**Release body:**
- Previously: just asset download instructions
- Now: includes "What's Changed" section with changelog entries for this release

**CHANGELOG.md location:**
- Previously: `docs/CHANGELOG.md`
- Now: `CHANGELOG.md` (repo root), copied into docs content during build

## Deployment and Testing

- [ ] Run build workflow with BUMP_PATCH (default)
- [ ] Run build workflow with BUMP_MINOR
- [ ] Verify changelog appears in release body
- [ ] Verify docs site includes CHANGELOG page

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/104

mise-tasks/doc-links

@@ -82,6 +82,14 @@ def main() -> int:
         else:
             ambiguous_filenames.add(filename)
 
+    # Special case: files at repo root that are copied into docs during build
+    # These are valid link targets even though they don't exist in docs/
+    REPO_ROOT = DOCS_DIR.parent
+    BUILD_TIME_DOCS = ["CHANGELOG.md"]
+    for filename in BUILD_TIME_DOCS:
+        if (REPO_ROOT / filename).exists():
+            valid_targets.add(Path(filename).stem)
+
     # Collect all broken and ambiguous links
     broken_links: list[tuple[str, int, str]] = []
     ambiguous_links: list[tuple[str, int, str, list[str]]] = []