Stabilize toolbar status layout

[onevtail]

What

• Reserve a bounded, compressible layout slot for the principal toolbar status area.
• Tail-truncate long status and PR/check summaries while preserving toast help and accessibility text.
• Add regression coverage for stable status width and single-line behavior under constrained width.

Why

The principal status view previously used its intrinsic content width, causing toolbar remeasurement and visible layout shifts when switching between idle hints, PR summaries, and toasts.

Fixes #471

How tested

• make check
• make build-app
• Focused ToolbarStatusViewTests (2 passing tests)
• make test (1,788 passing; one unrelated local ExternalDiffToolTests failure is blocked by a host Git identity hook)

— PR prepared by onevclaw on behalf of @onevcat

[Copilot]

Pull request overview

This pull request stabilizes the .principal toolbar status area by giving ToolbarStatusView a bounded, compressible layout slot and enforcing single-line tail truncation, eliminating layout shifts when the status content changes (idle hint ↔ PR summary ↔ toast).

Changes:

• Make ToolbarStatusView own a fixed ideal/max width (280pt) with single-line tail truncation, and preserve full toast text via hover help + accessibility labels.
• Remove duplicated outer horizontal padding from WorktreeDetailView call sites now that ToolbarStatusView applies it consistently.
• Add regression tests to lock in stable ideal width and single-line behavior under constrained width, plus update the user manual/docs sync metadata.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
supacodeTests/ToolbarStatusViewTests.swift	Adds regression coverage for stable fitting width and single-line truncation under constraint.
supacode/Features/Repositories/Views/WorktreeDetailView.swift	Removes duplicated horizontal padding around the principal status item.
supacode/Features/Repositories/Views/ToolbarStatusView.swift	Introduces bounded width + truncation and adds tooltip/accessibility text for toast messages.
supacode/Features/Repositories/Views/PullRequestStatusButton.swift	Ensures PR/check summary text tail-truncates within the constrained status slot.
docs/components/custom-actions.md	Documents the existing “first three commands inline, rest in overflow” behavior.
docs/components/canvas.md	Documents the bounded/compressible status area and truncation/hover behavior.
docs/.sync-meta.json	Updates docs sync baseline commit/date and note to reflect the manual verification.
docs-ai/README.md	Adds entry for the 046 toolbar status layout stability record.
docs-ai/046-toolbar-status-layout-stability/000-plan.md	Records the plan/constraints and chosen approach for the status slot stabilization.
docs-ai/046-toolbar-status-layout-stability/001-action.md	Records the implementation/verification log for the change.

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[onevcat]

暂时保留现状。参看 #471 评论