feat(orchestrate): move the bundled fleet into fleet.json

[Tryanks]

Summary

Orchestrate's bundled fleet (which models, their role, their guidance, the pre-discovery effort lists) moves from Rust constants into one data file parsed once in tcode-core. This is bundled data, not a plugin manifest: no loading, permission or host-API concepts.

 assets/orchestrate/
-├── astra.md
-├── fable-5-1.md
+├── fleet.json                       # models, roles, guidance, effort lists
 ├── workflow.md                      # unchanged
 └── collaboration.md                 # unchanged
 crates/core/src/settings/
+├── orchestrate_fleet.rs             # parse fleet.json once
+└── orchestrate_legacy.rs            # closed set of FNV-1a fingerprints of old bundled texts

Settings store overrides only.

OrchestrateChildModel::guidance
  if description is empty  → bundled guidance for this role and model
  else                     → the user's text
on patch
  if text == bundled guidance → normalize back to empty   # bundled prose never hits disk again
untouched row on the built-in endpoint
  carries bundled: <profile id> and follows that profile's model on load

One last migration. Every guidance text that older versions persisted as a bundled default is recognized by a frozen fingerprint set and collapsed to empty. The set is closed.

Behaviour changes for existing users

• A changed enabled / fast switch no longer pins an untouched row to its superseded model; it moves to the successor and keeps its switches.
• An untouched claude-opus-5 row merges into an existing claude-opus-5-5 row instead of sitting beside it.
• claude-opus-5 no longer has bundled guidance (main reused Opus 5.5's text for it).
• Clearing a description on a bundled model restores the bundled guidance; a bundled model can no longer be given "no guidance".
• Rows with an endpoint profile never track a bundled profile, so they do not follow model swaps.

Evidence

• Before / after prompt output: with default settings, render_orchestrate_configuration, compose_collaboration_brief and compose_orchestrate_text are byte-identical to main (40,017 bytes compared with cmp via a throwaway test, not committed).
• Tests: five migration tests kept with inputs rewritten as literal old-file JSON and assertions on the resulting fleet rather than stored text. Two deleted, their contract covered by orchestrate_recognizes_every_persisted_bundled_text, which is driven by the 18 texts extracted from main into tests/fixtures/orchestrate/persisted_bundled_texts.json. Added: rows store bundled guidance by reference; tracking rows follow their bundled profile.
• App: Settings → Orchestrate in a throwaway profile: default rows show bundled guidance, an edit persists across restart, restore returns the bundled text and the orchestrate section disappears from settings.json, add/remove works, an old-format file migrates. Light theme, one width; layout unchanged.

cargo fmt / clippy -D warnings / machete         ✓
cargo nextest run --workspace --locked           887 passed
Web / iOS / Android checks                       ✓

Not exercised: a live dispatch or collaboration against a provider.

Merge Danger

Door: one-way for settings on disk

Once a user's settings.json is normalized (bundled text collapsed to empty, bundled: markers added), an older build reads those empty descriptions as "no guidance". The fingerprint set is frozen, so texts persisted by this build cannot be re-recognized later.

Blast Radius: orchestrate-settings

PROTOCOL_VERSION 8 → 9; an older peer would see empty guidance. The behaviour changes above alter which model an untouched row lands on after an upgrade.