Add codemap progress to Agent Mode roots sidebar

[baron]

Summary

• Add a production-safe per-root codemap projection progress stream from accepted workspace codemap snapshots.
• Surface subtle per-root codemap status in the Agent Mode workspace roots sidebar, keyed by visible logical root UUID to avoid worktree cross-wiring.
• Keep progress updates separate from root rows to avoid row identity/order churn; global codemap disable overrides progress.
• Add focused sidebar/store seam coverage and ledger rows.

Notes

• Per-root codemap disable was investigated and intentionally deferred: CE currently has a global disable seam only; adding per-root disable needs persistence plus store/engine enforcement.
• The investigation note was kept out of the PR because repository guardrails classify docs/investigations/* as local agent-authored working documents unless explicitly allowlisted.

Validation

• make dev-format ✅
• make dev-swift-build PRODUCT=RepoPrompt ✅
• make dev-test FILTER=AgentWorkspaceRootsSidebarStoreTests ✅ (24 tests)
• make dev-test FILTER=WorkspaceFileContextStoreCodemapSeamTests/testAcceptedProjectionSnapshotsYieldRootProgressStreamEvents ✅
• make dev-lint ✅
• .agents/skills/rpce-contribution-check/scripts/preflight.sh commit ✅
• .agents/skills/rpce-contribution-check/scripts/preflight.sh push ✅

Known validation note

• make dev-test FILTER=WorkspaceFileContextStoreCodemapSeamTests (full suite) was attempted after rebasing onto latest main and failed in several unrelated existing tests/timeouts. The new focused seam test above passes.
• No visible app launch/relaunch was performed.