Some models / Ollama renderers occasionally emit tokenizer-level template
leaks that the existing regexes miss:
1. Malformed opening tags with no closing `>`, running straight into
user-facing content — e.g. `<think广场照明灯目前…` (observed with
Gemma 4 via Ollama). The earlier `<think>[\s\S]*?</think>` and
`^\s*<think>[\s\S]*$` patterns both require `>`, so these leak into
rendered messages.
2. Harmony-style channel markers like `<channel|>` / `<|channel|>` at
the start of a response.
3. Orphan `</think>` / `</thought>` closing tags left behind when only
the opener was consumed upstream.
Handles each case conservatively:
- Malformed `<think` / `<thought` only match when the next char is NOT
a tag-name continuation (`[A-Za-z0-9_\-:>/]`). Explicit ASCII class
instead of `\w` because Python's Unicode `\w` matches CJK and would
defeat the primary fix.
- Orphan closing tags and channel markers are stripped **only at the
start or end of the text**. `strip_think` is also applied before
persisting history (memory.py), so mid-text stripping would silently
rewrite transcripts where the tokens themselves are discussed.
Preserves: `<thinker>`, `<think-foo>`, `<think_foo>`, `<think1>`,
`<think:foo>`, `<thought/>`, literal `` `</think>` `` / `` `<channel|>` ``
inside prose or code blocks.
Adds 16 new regression tests covering both the leak cases and the
preserved-prose cases.
