fix(channels): strip <think> tags from streaming draft updates

[DaBlitzStein]

Summary

• Models like Qwen emit <think>...</think> reasoning blocks that were stripped from the final response via strip_think_tags() but leaked to users during partial streaming
• DraftEvent::Content and DraftEvent::Progress sent raw accumulated text to update_draft() without sanitization
• Add strip_think_tags_inline() to channels/mod.rs that strips think blocks from streaming draft text before sending to the channel
• Handles single blocks, multiple blocks, unclosed blocks (drops tail), and trims whitespace

Root cause

The existing strip_think_tags functions in compatible.rs, loop_.rs, and ollama.rs only operate on the final complete response. The streaming draft handler accumulates text chunks and sends them directly to the channel without any think-tag sanitization.

Test plan

• 6 unit tests for strip_think_tags_inline: single block, multiple blocks, unclosed block, no tags, empty string, whitespace trimming
• cargo clippy --all-targets -- -D warnings passes
• cargo fmt -- --check passes
• Manual test: Qwen model with stream_mode = "partial" no longer shows <think> content during streaming

[theonlyhennygod]

Comprehension Summary

What: Adds strip_think_tags_inline() to the streaming draft handler in src/channels/mod.rs, ensuring <think>...</think> reasoning blocks from models like Qwen are stripped before being sent to users during partial streaming updates.

Why: The existing strip_think_tags functions in compatible.rs, loop_.rs, and ollama.rs only operate on the final complete response. During streaming, raw <think> content leaked into DraftEvent::Content and DraftEvent::Progress updates sent to channels.

Blast radius: Streaming draft updates in process_channel_message(). No changes to final response handling, provider logic, or config schema.

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Review

Risk: risk: low — channels subsystem, additive sanitization function.

Verified:

• strip_think_tags_inline() correctly handles: single blocks, multiple blocks, unclosed blocks (drops tail), empty strings, and whitespace trimming.
• Applied to both DraftEvent::Progress and DraftEvent::Content paths.
• 6 unit tests cover all edge cases with clear assertions.
• The function uses simple string scanning (no regex) — efficient for streaming hot path.
• CI Required Gate is green across all platforms.
• PR template sections are filled out (summary format is compact but all key info is present).
• Privacy/data hygiene: pass.

Security/Performance Assessment:

• No security impact — sanitization only removes reasoning tokens from user-visible output.
• No performance impact — strip_think_tags_inline is O(n) with no allocations beyond the result string. Called per streaming chunk, which is acceptable overhead.

This PR is ready for maintainer merge.

Thank you for the clean fix and thorough test coverage.