Dock scanning panels in any of nine screen positions

[enaboapps]

Closes #874

Summary

• scan_panel gains a reusable Dock (column × row, each start/middle/end) that places the panel background in any of nine screen positions, plus shared position_rows / position_label helpers for a Position page.
• The keyboard and mouse panels replace their Dock top / Dock bottom toggle with a Position key that opens a 3×3 grid (Top left … Bottom right) and a Back key. The current position is marked with • and active styling. Choosing a position docks the panel there and returns to the page the user came from.
• point_workflow::Workflow owns one dock shared by both panels, so moving the mouse panel also moves the keyboard, and the position survives panels being rebuilt (reset, mode switches, config restart). It is not persisted across app restarts; no storage or protocol schema changes.
• Word predictions are hidden while the keyboard shows the Position page (new suggestion batches do not reset its scan) and return with Back.

Review

Independent agent reviews of 09659ea, f7f411e, and the integrated latest head 849f955 found nothing actionable. Follow-ups noted: the dock resets to Bottom when scanning restarts (not persisted, as before), and the Top right dock may sit under the Windows modifier chip overlay while modifiers are held.

Validation

• cargo fmt --check, cargo clippy --all-targets -D warnings: clean
• cargo test after merging current main: 542 passed (new: every-dock geometry, keyboard/mouse Position page, dock shared both ways between keyboard and mouse in workflow; keyboard work-area fit test now covers all nine docks × five scales × three pages)
• npm run lint, npm test (223 passed), npm run build: pass after merging current main
• PR head 849f955 resolves the overlap with Handle spacing and capitals for scanned punctuation #873 while preserving both the Position page and smart punctuation/automatic Shift behavior.

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