fix(streaming): prevent <think> in prose from suppressing response output

When the model mentions <think> as literal text in its response (e.g.
"(/think not producing <think> tags)"), the streaming display treated it
as a reasoning block opener and suppressed everything after it. The
response box would close with truncated content and no error — the API
response was complete but the display ate it.

Root cause: _stream_delta() matched <think> anywhere in the text stream
regardless of position. Real reasoning blocks always start at the
beginning of a line; mentions in prose appear mid-sentence.

Fix: track line position across streaming deltas with a
_stream_last_was_newline flag. Only enter reasoning suppression when
the tag appears at a block boundary (start of stream, after a newline,
or after only whitespace on the current line). Add a _flush_stream()
safety net that recovers buffered content if no closing tag is found
by end-of-stream.

Also fixes three related issues discovered during investigation:

- anthropic_adapter: _get_anthropic_max_output() now normalizes dots to
  hyphens so 'claude-opus-4.6' matches the 'claude-opus-4-6' table key
  (was returning 32K instead of 128K)

- run_agent: send explicit max_tokens for Claude models on Nous Portal,
  same as OpenRouter — both proxy to Anthropic's API which requires it.
  Without it the backend defaults to a low limit that truncates responses.

- run_agent: reset truncated_tool_call_retries after successful tool
  execution so a single truncation doesn't poison the entire conversation.

agent/anthropic_adapter.py

@@ -74,8 +74,11 @@ def _get_anthropic_max_output(model: str) -> int:
     model IDs (claude-sonnet-4-5-20250929) and variant suffixes (:1m, :fast)
     resolve correctly.  Longest-prefix match wins to avoid e.g. "claude-3-5"
     matching before "claude-3-5-sonnet".
+
+    Normalizes dots to hyphens so that model names like
+    ``anthropic/claude-opus-4.6`` match the ``claude-opus-4-6`` table key.
     """
-    m = model.lower()
+    m = model.lower().replace(".", "-")
     best_key = ""
     best_val = _ANTHROPIC_DEFAULT_OUTPUT_LIMIT
     for key, val in _ANTHROPIC_OUTPUT_LIMITS.items():