docs: add P2.16 backlog item for commit provenance / worktree-aware push events

Added new ROADMAP item to track the clawability gap around duplicate-looking
commit messages and worktree-originated push opacity in the build stream.

Pinpoint identified during dogfood: build stream doesn't show which worktree/
branch superseded which, causing confusion when parallel sessions push similar
commit messages from different worktrees.

Proposed fix: add worktree/branch metadata to clawhip push events and
de-dup superseded commits in build stream display.

ROADMAP.md

@@ -291,6 +291,8 @@ Priority order: P0 = blocks CI/green state, P1 = blocks integration wiring, P2 =
 14. **Config merge validation gap** — **done**: `config.rs` hook validation before deep-merge (+56 lines), malformed entries fail with source-path context instead of merged parse errors
 15. **MCP manager discovery flaky test** — `manager_discovery_report_keeps_healthy_servers_when_one_server_fails` has intermittent timing issues in CI; temporarily ignored, needs root cause fix
 
+16. **Commit provenance / worktree-aware push events** — clawhip build stream shows duplicate-looking commit messages and worktree-originated pushes without clear supersession indicators; add worktree/branch metadata to push events and de-dup superseded commits in build stream display
+
 **P3 — Swarm efficiency**
 13. Swarm branch-lock protocol — detect same-module/same-branch collision before parallel workers drift into duplicate implementation