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/skills.ts

@@ -1,6 +1,7 @@
 import { promises as fs } from 'node:fs';
 import { join, isAbsolute, basename } from 'node:path';
 import { pathGuard, PathScopeError } from './path_guard.js';
+import { stripQuotes } from '../utils/string-utils.js';
 
 // Batch 9.6: read-only skill library. Folders under /data/skills/<group>/<skill>/
 // contain a SKILL.md with YAML frontmatter (name + description) and a markdown
@@ -44,13 +45,6 @@ interface Frontmatter {
   description?: string;
 }
 
-function stripQuotes(s: string): string {
-  if (s.length >= 2 && (s[0] === '"' || s[0] === "'") && s[0] === s[s.length - 1]) {
-    return s.slice(1, -1);
-  }
-  return s;
-}
-
 function parseFrontmatter(yaml: string): Frontmatter {
   const fm: Frontmatter = {};
   for (const raw of yaml.split('\n')) {