feat: add markdown header support and info hints

[manthanabc]

This PR adds visual enhancements to improve user experience during AI interactions.

Changes

MarkdownWriter Header Support

• Added set_header() method to display status messages above markdown content
• Header is rendered above the buffer when streaming content
• Automatically cleared when not needed (e.g., after thinking phase completes)

Truncation Improvements

• Added dimming effect to top lines when content is truncated due to max_height
• Makes it visually clear that content has been truncated

Info Hints

• Added with_hint() method to Info struct for displaying additional context
• Hints are displayed at the end of info sections with a bullet point
• Currently shows 'Ctrl+O to view transcript' hint in conversation summaries

UI Enhancements

• Shows 'Thinking..' header during AI response generation
• Improved spinner comment clarity

Testing

• All 1373 tests pass
• Added new tests for markdown writer header functionality
• Added new tests for truncation dimming behavior

Co-Authored-By: Paws noreply@pawscode.dev

[Copilot]

Pull request overview

This PR enhances the markdown-based UI during AI interactions by adding header support, visual truncation cues, and contextual hints, while simplifying some spinner behavior.

Changes:

• Adds a header to MarkdownWriter with set_header() to show status text (e.g., “Thinking..”) above streamed markdown, and dims top lines when output is truncated by max_height.
• Extends Info with an optional hint and a with_hint() builder method, and displays the hint at the end of rendered info (e.g., “Ctrl+O to view transcript”).
• Updates UI call sites to use the new header/info behavior and clarifies spinner comments.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
crates/paws_main/src/ui.rs	Hooks the markdown header into thinking-phase UI and adjusts conversation summary display to use a title instead of a loading spinner.
crates/paws_main/src/info.rs	Adds hint support to Info, wires it into metrics summaries, and renders hints at the end of the info display with tests.
crates/paws_common/src/spinner/mod.rs	Updates spinner comment to match its actual output (no extra hint in the comment).
crates/paws_common/src/display/md/writer.rs	Adds header support, truncation dimming, and new tests to MarkdownWriter, and refactors streaming logic to work on String lines.

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[Copilot]

The add_chunk_dimmed path no longer applies the Attribute::Dim styling (the render call now passes None), so content that is intended to be dimmed is rendered with normal intensity while last_was_dimmed is still set to true. Either restore the dim attribute in this call or rename the method/flag and update callers if the behavior change is intentional, to keep the implementation and naming consistent.

Suggested change

	self.stream(&self.renderer.render(&self.buffer, None), spn);
	self.stream(&self.renderer.render(&self.buffer, Some(Attribute::Dim)), spn);