MS-26473 PDChat: input toolbar with model picker and separate read-aloud

[davidnmbond]

What

Every PDChat control now sits in one thin toolbar above the text box, which takes the full width: agent picker, model picker, notification sounds (moved out of the header), read-aloud, the microphone and Send. Maximise, restore and minimise stay in the header.

• IChatService.Models / SelectedModelId: a model picker, offered like agents (two or more).
• IChatService.IsReadAloudEnabled: off by default, independent of the microphone and of notification sounds, so all four sound combinations are possible. Read-aloud works without the microphone. The microphone pauses only while an answer is to be spoken.
• The microphone is an icon with an accessible name, with no text.
• Narrow (corner-docked) panels hide the picker labels with a container query and keep a single row.
• Demo: two models, and the second agent is renamed so it no longer reads like a voice option.

Verification

• All 3729 tests pass, including new ones for: the model picker; read-aloud with and without the microphone; turning read-aloud off mid-answer; all four mute/read-aloud combinations; the icon-only microphone; the toolbar layout; and notification sounds staying reachable when typing is not permitted.
• Headless Chrome render of the demo: the toolbar is one 28px row both corner-docked (350px) and full screen.

Part of MS-26473.

🤖 Generated with Claude Code

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 minor

Alerts:
⚠ 1 issue (≤ 0 issues of at least minor severity)

Results:
1 new issue

Category	Results
BestPractice	1 minor

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🟢 Metrics 36 complexity · 2 duplication

Metric	Results
Complexity	36
Duplication	2

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🟢 Coverage 100.00% diff coverage · +0.00% coverage variation

Metric	Results
Coverage variation	✅ +0.00% coverage variation
Diff coverage	✅ 100.00% diff coverage

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Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (737ce57)	15829	15816	99.92%
Head commit (88e8b95)	15856 (+27)	15843 (+27)	99.92% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#231)	44	44	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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