Make every selector in the thread first-prompt composer keyboard-operable
through the existing customizable keybindings system, alongside the
pre-existing modelPicker.toggle command:

- modelOptionsPicker.toggle (mod+shift+e): reasoning effort / traits menu
- runtimeModePicker.toggle (mod+shift+a): access level select
- planMode.toggle          (mod+shift+p): Plan/Build toggle
- environmentPicker.toggle (mod+shift+v): branch toolbar environment
- envModePicker.toggle      (mod+shift+l): local vs worktree
- branchPicker.toggle       (mod+shift+b): branch selector

All six are rebindable in Settings -> Keybindings (labels derived by the
existing commandLabel helper) and are upserted into existing configs by the
server's startup sync. Holding the platform mod key reveals Kbd hint badges
on each control via shouldShowComposerControlHintsForModifiers, which uses
subset (not exact) modifier matching so a bare Ctrl/Cmd reveals the chords.

Compact footer routes the effort/runtime toggles to CompactComposerControlsMenu;
mobile routes environment/env-mode to the combined run-context menu. Toggles
report availability so unavailable controls leave the browser default intact.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The hold-modifier hints were detached tooltips anchored below their
triggers, so they landed on the branch toolbar row underneath and
collided with the inline badges already rendered there. Render the
keycap in layout instead, taking over the disclosure chevron's slot: a
cap and a chevron are within a few pixels of each other, so the row
barely moves, the current values stay readable, and the composer and
toolbar rows finally use one treatment.

Labels now drop the platform mod key — Ctrl on Linux/Windows, Cmd on
macOS — which the user must already be holding for a hint to be visible
at all. `mod+shift+e` reads `Shift+E`. Subtraction is per binding rather
than a shared-prefix assumption, so a chord rebound to `mod+alt+e`
renders `Alt+E` beside its neighbours, and the label does not reflow as
further modifiers go down.

Also:

- `envModePicker.toggle` flips local <-> worktree directly instead of
  opening a two-item menu, matching `planMode.toggle`. Clicking still
  opens the menu, which is what surfaces the worktree path.
- The environment and workspace indicators explain themselves while
  inert, distinguishing a thread that has already started from a project
  with only one environment. They previously rendered as muted,
  chevron-less controls that silently did nothing.

The caps dropped the platform mod key on the grounds that the user was
already holding it. That reasoning was sound when a cap read `Shift+E`
and every pixel counted, but the Apple glyphs shrank the full chord to
`⌃⇧E` — about 8px wider than `⇧E` — so the saving no longer pays for
making the reader reconstruct which modifier the hint belongs to.

Showing the whole chord also matches how macOS menus print shortcuts,
and it removes a function: the per-command gate already decides whether
a hint is visible, so the label is now just `shortcutLabelForCommand`.