v2.4.1-sidecar-routing: route per-agent flags to llama-sidecar + tool gap fix

Batch 3c: when an agent has llama_extra_args in AGENTS.md, provider.ts
routes inference through LLAMA_SIDECAR_URL instead of LLAMA_SWAP_URL.
X-Agent-Flags header built from the agent's flags. Boot-time guard
refuses to start if any agent has llama_extra_args but LLAMA_SIDECAR_URL
is unset. PrefixFingerprint gains a route field (swap/sidecar) for
per-turn visibility. 9 provider tests.

AGENTS.md tool gap: all agents (except Prompt Builder) were missing 8
tools that were added after the original tool lists were written:
request_read_access, view_truncated_output, ask_user_input, git_status,
get_blast_radius, get_hot_files, get_middleware, get_routes. The missing
request_read_access caused silent "permission denied" when reading files
outside the project root.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/server/src/config.ts

@@ -25,6 +25,8 @@ const ConfigSchema = z.object({
   // v2.0.5: cheaper model for titles, summaries, labeling. Falls back to
   // session model (auto_name) or DEFAULT_MODEL when unset.
   FAST_MODEL: z.string().optional(),
+  TASK_MODEL_URL: z.string().url().optional(),
+  LLAMA_SIDECAR_URL: z.string().url().optional(),
 });
 
 export type Config = z.infer<typeof ConfigSchema>;