feat: list all Codex models in /orch and add Qwen 3.8 Cerebras row

[Desperado]

Why

After v1.31.0, the /orch picker's Codex section offered only two entries (Codex default, GPT 6 Astra) even though the runner allowlist supports eight models. This PR exposes all of them and pre-adds Qwen 3.8 to the Cerebras section.

Changes

• internal/tui/tui_backend.go — codexModels now lists every codexrunner.SupportedModels() entry (GPT 6 Astra, 5.6 Sol/Terra/Luna, 5.5, 5.4, 5.4 Mini, 5.3 Codex Spark) with external badges; Codex default keeps ⭐/shortcut 6.
• internal/tui/tui_backend_cc_test.go — new TestPickerOffersEverySupportedCodexModel fails when the picker and the runner allowlist drift in either direction.
• internal/api/cerebras.go — CerebrasQwen38Model = "qwen-3.8" constant plus qwen/qwen3.8/qwen-3-8 alias resolution (unknown IDs still pass through).
• internal/api/cerebras_test.go — alias table coverage.

⚠️ Follow-up at Qwen 3.8 launch

The Cerebras model catalog page was not reachable at authoring time, so qwen-3.8 follows Cerebras naming (zai-glm-4.7, gemma-4-31b) but is unconfirmed against the live API — per AGENTS.md the model is not live yet. The picker row is labeled coming soon; verify the real ID before launch.

Verification

go build -o qmax-code .   # pass
go vet ./...              # pass
go test ./...             # all packages ok

Risk: LOW — additive picker rows and alias cases; persisted codex_model values are validated against the same allowlist on startup.

[sigilix]

Phase: Synth
Commit: caf4d78
Specialists: 4/4 completed
Dispatched: logic, security, performance, tests
Completed: logic, security, performance, tests
Graph context: none; 0/4 files; 0 nodes

Sigilix is reviewing this pull request.

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