Split Skywalker identity from the worker overlay

[TheGreatAxios]

Summary

• Skywalker identity (name, stance) is separate from the orchestrator overlay.
• Leaf directors receive a worker overlay, not closed-fleet / never-implement / spawn-graph rules.

Verification

• bun test ./src/agent/directors ./src/agent/prompts.test.ts ./src/prompts.test.ts ./src/subagent passes (460 tests)

Fixes CL-6552

[linear-code]

CL-6552

[TheGreatAxios]

Not merging.

The identity/overlay split is a real prompt problem, but this PR is not the win:

• Grok 4.5 pass-rate is tied with main 0.2.99 at ceiling (13/13 overlapping cells, n=1). This suite cannot show a grok lift.
• The cell that can move, GPT Luna simple-health, regresses: main PASS 8/20 vs this tree FAIL OVER_BUDGET 27/20 (n=1).
• Terra on this tree also blows simple-health (21/20) and rename-user (32/25).

Scoreboard: https://linear.app/abklabs/document/capability-eval-tracking-9a14c0448561

Park the overlay rewrite. If we retry, the gate is Luna simple-health vs main, same provider/model, not another grok matrix.