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>

apps/server/src/services/message-columns.ts

@@ -0,0 +1,15 @@
+// Shared column projections for queries against the messages_with_parts view.
+// All sites that read the full Message wire shape for route responses use
+// MESSAGE_COLUMNS. The inference load path uses INFERENCE_MESSAGE_COLUMNS —
+// it adds reasoning_parts but omits the compaction-display fields
+// (summary, tail_start_id, compacted_at, model) that only the UI needs.
+
+export const MESSAGE_COLUMNS =
+  'id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq, ' +
+  'tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata, ' +
+  'summary, tail_start_id, compacted_at, model';
+
+export const INFERENCE_MESSAGE_COLUMNS =
+  'id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq, ' +
+  'tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata, ' +
+  'reasoning_parts';