[WRONG BRANCH] fix(codex): restore collaboration prompt mapping

[luvs01]

Motivation

• A prior change removed the known collaboration_mode tag mapping and classified collaboration as permanently unmapped, which hid collaboration instructions when Codex actually rendered them.
• Collaboration is a context-dependent config-toggle and an absent section should be reported as not-rendered, not not-exposed, so the inspector must preserve the mapping.

Description

• Restores the collaboration: "collaboration_mode" entry in LAYER_SECTION_TAGS and removes collaboration from UNMAPPED_LAYER_IDS in src/codex/prompt-text-probe.ts.
• Adds a focused projection helper mapSectionsToLayers and exports it as mapSectionsToLayersForTests, and updates probePromptText to use that helper for mapping sections to layers.
• Adds regression coverage in tests/codex-prompt-text-probe.test.ts that asserts a rendered <collaboration_mode> maps to the collaboration layer with correct text/byte count and that an absent section maps to not-rendered.

Testing

• Ran bun test tests/codex-prompt-text-probe.test.ts; the focused probe tests passed (all assertions succeeded).
• Ran bun run typecheck (bun x tsc --noEmit) which completed with no type errors.
• Executed the full test suite with bun run test; the focused probe tests passed in that run, while some unrelated tests in this environment failed (these failures are orthogonal to the probe change).

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Codex Task

[github-actions]

✅ Deterministic PR hygiene checks passed.

[github-actions]

⏳ DRAFT

• wrong target branch (main); retarget to dev.

What to do

• Retarget this PR to dev — all contributions go to dev.

Its title has been prefixed with [WRONG BRANCH].
This pull request was already a draft. Its draft status will be preserved after every issue above is resolved.

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