fix(chat): always think on qwen3, drop content-based classifier

Content-based gating (_should_think) was introduced in 87fcaa6 to cut
TTFT on simple prompts, but it has no way to tell that short prompts
like "create a task titled X" are going to trigger a tool call — and
qwen3:14b's tool-call template is unreliable at think=False, producing
intermittent silent generations where output tokens burn but nothing
parses into content or tool_calls.

Reverting to always-on thinking restores the pre-87fcaa6 reliability
of tool emission at the cost of TTFT latency on short conversational
prompts. This also lets us delete the silent-round retry loop (which
can no longer fire) along with its bookkeeping.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/architecture.md

@@ -313,7 +313,7 @@ See [sso-oauth.md](sso-oauth.md) for provider-specific setup instructions.
 
 ### Tool Routing
 
-No separate intent router — the main model handles all tool routing directly via Ollama's structured tool-calling output. The model receives the full tool schema list and decides whether to call a tool or respond conversationally. A thinking-mode heuristic (`_should_think()`) detects complex prompts and enables extended reasoning.
+No separate intent router — the main model handles all tool routing directly via Ollama's structured tool-calling output. The model receives the full tool schema list and decides whether to call a tool or respond conversationally. Extended reasoning (`think=True`) is always on for qwen3-class models: content-based gating was tried but exposed tool-call template fragility on short tool-intent prompts.
 
 ### Tool Loop