v0.13.5 — REPL Mode Switch Restored

Versions step by 0.0.5 from here on: 0.13.5, 0.14.0, 0.14.5, and so on.

Added

• :gazelle and :coder work in the ordinary REPL again. Restored
  unchanged from v0.13.1, which was withdrawn on suspicion of causing a task to
  loop on one step. It wasn't: 0.13.0 traced that to step-3.5-flash collapsing
  into repetition inside a single streamed reply, with nothing in the harness to
  stop it. The mode branch never ran in coder mode — it was inert while
  replMode === 'coder', and the coder path beneath it was untouched — so with
  the real cause fixed there is nothing left to hold it back.

  :help and the README have advertised both commands since Gazelle landed,
  while only the --gazelle orchestrator implemented them; typed into the plain
  REPL they fell through the command handler and were sent to the model as a
  task. Now the TUI switches in place: the machinery of a Gazelle turn lives in
  agent/gazelle-chat.ts, independent of how input arrives, so the TUI can drive
  it without opening a second readline on stdin it already holds in raw mode
  (two readers on one stream double every keypress). Lean turns share the REPL's
  conversation — carried both ways, coder tool noise stripped on the way in —
  count against the session token ceiling, and appear in /stats; the status
  line gains a gazelle marker. A mode switch or second message arriving while a
  reply is still streaming waits for it rather than interleaving two
  conversations into one history.

  The commands live in cli/repl-mode-commands.ts because nothing in
  cli/index.ts can be imported by a test, which is how a command stayed
  advertised and unimplemented without anything going red. One of the tests walks
  :help's Modes section and asserts every command it lists is handled.