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/web/src/components/ProjectSidebar.tsx

@@ -29,6 +29,7 @@ import { usePullToRefresh } from '@/hooks/usePullToRefresh';
 import type { SidebarProject, WorktreeRiskReport } from '@/api/types';
 import { giteaUrlFor } from '@/lib/projectUrls';
 import { isCoderSessionName } from '@/lib/coder-session';
+import { relTime } from '@/lib/format';
 import { cn } from '@/lib/utils';
 
 const EXPANDED_KEY = 'boocode.sidebar.expanded';
@@ -54,22 +55,6 @@ function writeExpanded(ids: Set<string>): void {
   }
 }
 
-function relTime(iso: string): string {
-  const now = Date.now();
-  const t = Date.parse(iso);
-  if (Number.isNaN(t)) return '';
-  const sec = Math.max(0, Math.floor((now - t) / 1000));
-  if (sec < 60) return `${sec}s`;
-  const min = Math.floor(sec / 60);
-  if (min < 60) return `${min}m`;
-  const hr = Math.floor(min / 60);
-  if (hr < 24) return `${hr}h`;
-  const day = Math.floor(hr / 24);
-  if (day < 30) return `${day}d`;
-  const mo = Math.floor(day / 30);
-  if (mo < 12) return `${mo}mo`;
-  return `${Math.floor(mo / 12)}y`;
-}
 
 function activeProjectId(
   pathname: string,