fix: open the composer's /, @ and $ menus on the phone

[Tryanks]

Summary

Typing /, @ or $ in the composer on a phone now opens the same trigger menu as on the desktop, and /later schedules the turn instead of being sent to the agent as literal text.

Two guards from the first mobile client (#329) were responsible. Both are removed and nothing is added.

 Composer::recompute_trigger
-  if self.compact { clear active_trigger; return }
   compute trigger from the text before the cursor

 Composer::submit
-  if parse_later(text) && !self.compact
+  if parse_later(text)
     schedule the turn

compact is is_mobile && compact_for(width), so desktop builds were never affected. The menus' data was already protocol-backed (provider commands, Query::ListActiveWorkspace, Command::ScheduleTurn), so a remote phone needs nothing else.

Evidence

• Before: on the phone, typing / showed nothing and /later … went to the agent as text.
  After: cargo run -p tcode-ui --example phone against a throwaway headless host: / lists the built-in commands, /plan switches mode, @ lists and inserts remote files.
• Test: the_phone_composer_opens_the_same_trigger_menus builds the composer as the phone does at 393×852, types / and @ through the window input handler, draws, and asserts the first menu row is laid out. It fails with the guard restored. No test owned this contract before.

cargo fmt / clippy --workspace -D warnings     ✓
cargo nextest run -p tcode-ui --locked          288 passed

Merge Danger

Door: two-way

Two lines of guard removed; trivially revertible.

Blast Radius: phone-composer

Not exercised on a real device: iOS and Android soft keyboards (including CJK IME composition of /), menu placement with the keyboard up, touch taps on menu rows, and provider-native commands or $ skills on the phone. On mobile Return inserts a newline, so a row is accepted by tap.