GODM-47: Fix the folder picker footer overlap and long-path clipping

[danielehrhardt]

What does this change?

Fixes GODM-47: the "Work in a folder" dialog broke as soon as the folder name got a little longer.

The footer held the keyboard hints, the native picker button, Cancel and Use in one row. The hints were allowed to shrink below their own width, so in the desktop app they slid under "Open Finder…", and the folder name in the Use button was cut off at 11rem.

• Footer is one row of actions: the native picker on the left, Cancel and Use on the right. Use shows the full folder name (truncates only past ~17rem) and its ⌘↵ shortcut.
• Enter / Backspace hints moved to the filter row and show while the filter is empty.
• "Can't use this folder" notice sits above the footer inside the fixed-height list area, so the dialog keeps its size when it appears (Home shows it by default, because it contains the data directory).
• Deep paths no longer clip the dialog. The dialog's grid column could grow past the dialog, so a long breadcrumb pushed Cancel and Use out of view. This also affected phone-width viewports.
• The description is left-aligned on phones, like the title.

Only apps/desktop/src/components/chat/folder-picker.tsx changes. docs/screenshots/folder.png still shows the old hint strip in the footer.

How was it tested?

• pnpm typecheck, pnpm test (1393 pass, 0 fail), pnpm --filter @godmode/desktop build
• Rendered the dialog against a local core in WebKit and Chromium with the Tauri shell stubbed, and measured the footer for overlap and overflow in each state: short, 26- and 57-character folder names, a path seven levels deep, Home (blocked), light and dark, macOS and Windows labels, 1280px, 400×560 (the minimum window) and 375px wide.
• Before: the ⌘↵ hint overlaps "Open Finder…" and the name is clipped; with a deep path the footer is 726px wide inside a 576px dialog. After: no overlap or overflow in any state, and the dialog height stays 579px with and without the notice.
• Not run in the packaged Tauri app itself.

Checklist

• pnpm typecheck and pnpm test pass
• cargo clippy / cargo test pass (if apps/desktop/src-tauri changed) — not changed
• API changes are reflected in packages/shared and apps/desktop/src/lib/api.ts — none
• No secrets, tokens or personal data in code, fixtures, logs or screenshots
• Docs updated where behaviour changed — docs/screenshots/folder.png not regenerated