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/config.ts

@@ -18,7 +18,6 @@ const ConfigSchema = z.object({
   GITEA_BASE_URL: z.string().url().default('https://git.indifferentketchup.com'),
   GITEA_USER: z.string().default('indifferentketchup'),
   GITEA_TOKEN: z.string().optional(),
-  GITEA_SSH_HOST: z.string().default('100.114.205.53:2222'),
   // v1.15.0-mcp-multi: path to the MCP config JSON file. Default /data/mcp.json
   // (bind-mounted alongside AGENTS.md). File missing = no MCP (opt-in).
   MCP_CONFIG_PATH: z.string().optional(),