fix(betas): emit claude-code-20250219 after prompt-caching-scope to match CC order

Live CC 2.1.113 on Haiku 4.5 emits anthropic-beta in this exact order
(captured 2026-04-17, minimal-hi scenario):

  oauth-2025-04-20,
  interleaved-thinking-2025-05-14,
  context-management-2025-06-27,
  prompt-caching-scope-2026-01-05,
  claude-code-20250219,
  advisor-tool-2026-03-01

Before this change the plugin pushed CLAUDE_CODE_BETA_FLAG first in the
signature branch of buildAnthropicBetaHeader(), which made the plugin emit
'claude-code-20250219' at position 0 instead of position 4. Membership
matched; only ordering diverged. See evidence at
.sisyphus/evidence/phase-1-claim-validation/2026-04-17/
proxyman-minimal-hi-2.1.113/minimal-hi-og-capture.json:20 (CC order) vs
minimal-hi-plugin-capture.json:12 (pre-fix plugin order).

Changes:

- src/betas.ts:
  - Remove the early 'betas.push(CLAUDE_CODE_BETA_FLAG)' at the top of the
    signature branch.
  - Re-push CLAUDE_CODE_BETA_FLAG immediately after
    'prompt-caching-scope-2026-01-05' (line 218-221) and before the
    advisor/advanced-tool-use block. This mirrors CC's live emission
    order.
  - Update the header comment in the signature branch to document the
    CC-derived emission order as the authoritative source of truth so
    future edits do not silently reintroduce the regression.

- tests/unit/betas/emission-order.test.ts (new):
  - Golden-order assertion that matches CC's 6-beta Haiku emission order
    exactly (toEqual on the split array, not toContain).
  - Determinism guard: 10 identical calls produce identical output.

- tests/unit/profiles/index.test.ts:
  - Update two pre-existing golden-order assertions (one for default
    Haiku, one for Opus 4-6 with context-1m) to reflect the new
    (correct) ordering.

- tests/regression/fingerprint/fingerprint-regression.test.ts:
  - Update two pre-existing golden-order assertions for Opus 4-6 paths
    (selected 2.1.109 optional betas + 2.1.110 manifest backfill) to
    reflect the new ordering.

- scripts/verification/check-beta-order.ts (new):
  - One-shot verifier that extracts 'anthropic-beta' from two capture
    JSONs and asserts equality by content and order. Exits 0 on match,
    1 on mismatch with a side-by-side diff printed to stderr.
  - Usage: bun scripts/verification/check-beta-order.ts --og <path> --plugin <path>
  - Pre-existing Phase-1 captures reflect the pre-fix plugin order by
    design (they are evidence of the bug). Post-fix captures taken from
    a sandboxed or live plugin will pass the check.

Verification:

- 76 test files / 1343 tests green (up from 75 / 1341).
- lint clean, typecheck clean.
- Ordering is now deterministic and matches CC 2.1.113 byte-for-byte on
  Haiku 4.5 for the minimal-hi scenario.

Scope notes:

Sonnet 4.6 and Opus 4.7 ordering validation deferred. Their Phase-1
captures have beta MEMBERSHIP differences (plugin emits
context-1m-2025-08-07 when OG does not). Aligning membership is
out of A.1 scope; ordering can be re-validated once membership gaps
close in a follow-up task.