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/model-context.ts

@@ -18,8 +18,6 @@
 
 export interface ModelContext {
   n_ctx: number;
-  total_slots: number;
-  fetched_at: number;
 }
 
 const NEGATIVE_TTL_MS = 60_000;
@@ -77,19 +75,13 @@ export async function getModelContext(model: string): Promise<ModelContext | nul
     }
     const body = (await res.json()) as {
       default_generation_settings?: { n_ctx?: number };
-      total_slots?: number;
     };
     const n_ctx = body?.default_generation_settings?.n_ctx;
     if (typeof n_ctx !== 'number' || n_ctx <= 0) {
       negativeCache.set(model, Date.now());
       return null;
     }
-    // total_slots is informational; default to 1 if missing rather than
-    // reject the whole response. Most local llama-swap setups run a
-    // single slot anyway.
-    const total_slots =
-      typeof body?.total_slots === 'number' && body.total_slots > 0 ? body.total_slots : 1;
-    const entry: ModelContext = { n_ctx, total_slots, fetched_at: Date.now() };
+    const entry: ModelContext = { n_ctx };
     positiveCache.set(model, entry);
     // Clear any stale negative entry so a future query sees the positive
     // hit cleanly (otherwise the negative TTL never expires from the map).