docs: align remaining alloc-failure references with ADR-010 §2A (prepublish review for v0.3.0)

- README.md ADR index: ADR-010 status notes the §2A amendment
- ADR-009: amendment note records the §2A supersession (in-band path
  shrinks to nothing from registered producers)
- ADR-010 Consequences: dial_failed replaces the stale in-band
  allocate_failed retry-policy bullet
- AllocFailed doc comment + tty-backend.md: describe both failure
  surfaces (direct-path frame / channels-path dial_failed)

docs/architecture/decisions/010-channels-establisher-migration.md

@@ -242,8 +242,9 @@ on `establishment_reason()` without unwrapping strings.
   open no longer allocates → succeeds → in-band-fails. Ledger, policy
   count, and manager state balance on every rejection.
 - Retry policy / UX can branch: `unknown_resource` (bad config — don't
-  retry), `timeout` (maybe retry), `allocate_failed` (capacity —
-  still distinguishable in-band).
+  retry), `timeout` (maybe retry), `dial_failed` (capacity/target
+  refused — maybe retry; amended §2A, was the in-band
+  `allocate_failed`).
 - The consumer's `open_via_channels` failure is a typed call error —
   no peeking at the data stream for anything but the (now
   unreachable-from-registered-producers) error-frame formality.