feat(#17): TUI Bifrost-bind trigger (slice 3b of the INV-008 lockstep)

Slice 3b of issue #17 — the TUI surface of the bind trigger (web is 3c). The TUI
consumes the same ParsedArgs the cli already parses (--bifrost-plane / --bifrost-url
/ consumer key from RATATOSKR_BIFROST_CONSUMER_KEY), so this wires the bind into
_resolve_then_run's pre-flight create_session:

- bifrost + consumer_key threaded into create_session at the pre-alt-screen
  resolution layer, so bind failures land on the operator's REAL stderr BEFORE
  the Textual alt-screen opens (INV-002, mirrors issue #6's pre-alt-screen
  routing) — never eaten by the alt-screen teardown.
- BifrostConsumerKeyMissing -> exit 22; BifrostHandshakeFailed -> exit 23 with the
  same 401-scoping hint, keyed on bifrost_error == bifrost.auth_rejected. Exit
  codes + label vocabulary match cli._amain exactly (INV-006).
- Bound-state indicator on success (pre-alt-screen): ". bifrost: status=bound
  plane=... endpoint=...".

3 new TUI bind tests (handshake-fail / consumer-key-missing / bound-create carries
binding + indicator, run_async stubbed). Full suite 465 green; added lines ruff +
mypy clean (pre-existing tui.py lint/type backlog untouched per surgical-changes).

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "ratatoskr"
-version = "0.17.10"
+version = "0.17.11"
 description = "Worldtree Conversation API debug TUI — multi-pane observability dashboard"
 readme = "README.md"
 requires-python = ">=3.12"