desktop: Soft Tactile overlays — palette, sheets, alert, toasts, persisted theme

[plombeer31]

Part of the Soft Tactile desktop redesign. Depends on #440 (base branch facelift/1-foundation); every region PR can merge in any order after it. The integrated build is facelift/integration.

Soft Tactile, overlays (SH-03, SH-10…16). Builds on the foundation PR.

What changes

• Command palette: 620px, radius 24, blurred scrim; 56px input row with the esc keycap; sentence-case groups; 36px rows (icon · bold title · context · keycaps or mono slash alias); brand-tint selection; footer ↩ Go · ↑↓ Move · N commands.
• Query and no match: typed part bold; matching chats, tasks and skills under their own headers with state dots; "No results for “q”" with the "Ask the agent" row.
• Theme scope: "Theme ×" chip, laptop / sun / moon rows, a check on the current theme, ⌫ Back.
• Theme persists across launches: the choice is stored in the renderer's localStorage and re-applied before the first paint. System removes the override.
• Switch session and shortcuts sheets: radius 24, header, body, footer; 46px session rows with the sidebar's dot grammar. The shortcuts sheet no longer lists session-wide approval grants (the HTTP API only allows once or denies).
• Delete alert: centred card with the app mark; Cancel really has focus on arrival; Delete is the destructive fill.
• Toasts: lifted cards with a round green check or red alert, bold title and caption.

Verified

• Trusted-input driver, 40/40: palette from the Search pill and ⌘K, query, Enter into the Theme scope, both ways out of it, Dark applied; ⌘O and ⌘/ sheets and their close paths; alert focus, Enter / Esc / backdrop / Cancel; real toasts from Copy and from ⌘0 on a narrow window; relaunch opens in the stored theme.
• Smoke on the merged build: same 4 known failures as a0811bc3.