Lift deep-research hard timeout into a setting (#783)

The 600s wall-clock cap in research_handler.start_research was too short
for local / edge LLMs to finish a deep-research synthesis — long
extraction passes plus a slow final report routinely blew past 10
minutes and the run was killed with partial results.

Introduce research_run_timeout_seconds (default 1800s = 30 min) in
DEFAULT_SETTINGS and resolve it at start_research entry when the caller
hasn't pinned hard_timeout. Bound the resolved value at [60, 86400] so a
misconfigured settings.json can't either disable the safety net or
explode into a multi-day hang. Existing call sites in research_routes.py
and chat_routes.py keep working unchanged — they don't pass hard_timeout
and now pick up the new default.

Closes #595.

src/settings.py

@@ -66,6 +66,11 @@ DEFAULT_SETTINGS = {
     "research_max_tokens": 16384,
     "research_extraction_timeout_seconds": 90,
     "research_extraction_concurrency": 3,
+    # Hard wall-clock cap on a single deep-research run. The previous 600s
+    # (10 min) default cut off slow local / edge LLMs mid-synthesis; 1800s
+    # (30 min) is comfortable for most local setups while still bounding
+    # runaway jobs. Tune via Settings or by editing data/settings.json.
+    "research_run_timeout_seconds": 1800,
     "agent_max_tool_calls": 0,
     "agent_input_token_budget": 6000,
     "agent_stream_timeout_seconds": 300,