chore: bump fallback version to v0.16.0 for release

40 commits since v0.15.2 (2026-03-09): 20 fixes, 6 features, 7 chores, plus
docs/tests. Minor bump because of the feature work (robot registry phase
three, --graph-root subgraph triage, hybrid search with graph-aware
ranking, heatmap controls + dynamic force layout, JSONL reader +
IssueReader interface, bd workspace bridge).

Notable user-facing fixes in this range:
- #142 graph node side panel pins reliably on click (bv-142)
- Spurious "Error handling --robot-*" banner on success (bv-142 follow-up)
- Cache race hardening, deep-copy snapshot tree, CLI flag validation
- XSS escape title, OPFS cache invalidation, cache-busting for Pages updates
- JSONL tombstone filtering, SQLite DATETIME parsing, graph heatmap legend

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Dicklesworthstone

pkg/version/version.go

@@ -14,7 +14,7 @@ var version string
 
 // fallback is the hardcoded version kept in sync with the latest release tag.
 // Used only when both ldflags and debug.ReadBuildInfo fail to provide a version.
-const fallback = "v0.15.2"
+const fallback = "v0.16.0"
 
 // Version is the resolved application version, populated by init().
 var Version string