[matthewrball]

Add Start from scratch to the project picker so a new task can begin without choosing an existing folder. Selection preserves the draft and creates nothing; the first message creates a fresh persistent folder on the selected computer, registers it as Untitled project, and starts the task with that explicit project root.

Keep the picker compact, with Start from scratch and Choose folder above at most three recently used projects across connected computers. Rank by explicit project/task selection and accepted messages, preserve the sidebar’s manual order, and show local results without waiting for a slow remote computer. Preserve draft text, attachments, and model choices during setup, reject stale navigation results, and require remote computers to advertise support. Folder creation never overwrites existing files or deletes files after a later failure.

Preview (native UI, sample projects):

Full-window context (combined native preview, sample projects):

This view also includes the sidebar styling from #1347 and composer placement from #1353. Those changes are outside this PR.

Validation:

• App suite on macOS with Rust 1.96.0: 1,156 passed, 0 failed, 2 ignored.
• Project/runtime regression tests: 83 passed, including recency beyond the first navigation page, account isolation, and accepted versus rejected sends.
• Formatting, Git metadata, and packaging checks passed.
• Independent source review found no remaining defects.
• just ci stops at strict Clippy with 26 diagnostics on unchanged source under the installed toolchain; pinned-toolchain CI remains pending.
• Tested in a local build, including the project picker and three recent projects. The signed-in first-message/inference flow still needs validation by a maintainer with Dev access.

Maintainer validation needed: I do not have a Dev account. Please test the signed-in Start from scratch flow in Dev: select Start from scratch, send the first message, and confirm that a fresh project folder is created, the task uses that folder, and a model response arrives.

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