refactor: codebase audit cleanup — dead code, dedup, module splits

Multi-agent audit + aggressive cleanup across server/web/coder/booterm,
delivered behind a DEFER discipline so none of the in-flight files were
touched. Removes dead code/deps/columns, dedups server + coder helpers,
and splits the oversized modules (tools.ts, opencode-server.ts,
sentinel-summaries, turn.ts, TerminalPane.tsx) behind stable contracts.
Adds 78 parity/unit tests (server 587, coder 323); fixes two latent bugs
(ChatPane queue keys, FileViewerOverlay blank-line parity).

Intended tag: v2.7.12-audit-cleanup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CURRENT.md

@@ -1,10 +1,9 @@
 # Current focus
 
-Last updated: 2026-05-26
+Last updated: 2026-06-02
 
-- **Batch:** v2.3-provider-lifecycle (openspec drafted; not started)
-- **Branch:** `main`
-- **Blockers:** none
-- **Last shipped:** `v2.2.2-xml-placeholder-reject`
+- **Last shipped:** `v2.7.8-ember-coder-tabs-model-chips` (2026-06-01)
+- **Branch:** `codebase-audit-cleanup` (audit + cleanup epic, off main HEAD)
+- **In progress:** Phase 3 — stale comments + docs refresh
 
-Update this file when starting or finishing a batch. Agents: read this first for session intent; if stale vs `CHANGELOG.md`, trust CHANGELOG for shipped state.
+See `CHANGELOG.md` for the full shipped history. That file is always authoritative; this file is a quick orientation pointer only.