keyboard: guard g-leader and j/k against palette and editable targets

Add an early return after the ⌘K and Esc handlers so the g-prefix
dispatch, g-start, j/k cursor, and Enter activation skip when the
palette is open or the focused element is an input/textarea/contenteditable.
Without it, typing "gh" into the palette search input fires go("home")
mid-query, navigating away while the palette stays open.

Two regression tests added: g+h with palette open → no navigation; g
on a focused input → no pending state, follow-up h does nothing.

web: shell, theme, keyboard, stub routes, palette skeleton

- lib/theme.ts: bootstrapTheme() + setTheme() with OS/localStorage sync
- lib/keyboard.ts: g-prefix nav, j/k cursor, ⌘K palette, Esc, Enter
- lib/theme.test.ts + lib/keyboard.test.ts: 26 vitest tests (TDD)
- shell/TopBar.tsx: brand crumb, search trigger, tab nav using router pathname
- shell/SubBar.tsx: slot component with optional right section
- shell/Palette.tsx: modal overlay, JUMP items, synthetic SEARCH row
- styles/shell.css + styles/palette.css: ported verbatim from prototype.css
- routes/__root.tsx: wires TopBar, Outlet, Palette, keyboard controller, bootstrapTheme
- routes/index.tsx + projects/stats/health/settings/search.tsx: EmptyState stubs
- main.tsx: replace scaffold div with RouterProvider
- vitest.config.ts: add jsdom url for localStorage support (Node 25 compat)