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/inference/parts.ts

@@ -1,11 +1,10 @@
 import type { Sql } from '../../db.js';
 import type { ToolCall, ToolResult } from '../../types/api.js';
 
-// v1.13.0: dual-write helper. Every site that writes the legacy
-// messages.tool_calls / messages.tool_results JSON columns calls into here
-// to mirror the same data into message_parts rows. Reads still go to the
-// JSON columns; the swap to parts-as-source-of-truth happens in a later
-// v1.13 dispatch alongside the AI SDK streamText migration.
+// v1.13.0: message_parts write helpers. v1.13.20: legacy tool_calls/
+// tool_results JSON columns dropped; message_parts is the sole source of
+// truth. All writes go through insertParts / partsFromAssistantMessage /
+// partsFromToolMessage. Reads use the messages_with_parts view.
 
 // v1.13.13: 'synthesis' added. Schema CHECK constraint is updated in lockstep
 // (schema.sql adds 'synthesis' to message_parts_kind_chk on startup). The