feat: add controlled production-send mutation envelope

[andrei-hasna]

Summary

• add emails send-controlled apply|readback with only private descriptor path, opaque request id, and receipt path as public inputs
• validate owner-only regular files before send, use the existing server-owned idempotency API, and atomically publish complete mode-0600 no-overwrite receipts
• keep private message fields and idempotency keys out of argv, output, receipts, structured logs, and controlled-path errors
• preserve the existing inline emails send command

Task

• UST-00144
• Todos UUID: 99d59165-610c-42cf-8c84-aec405c064a8

Exact candidate

• base: 5db888d7a8d3be326bd67d64f7c48c918abc62a2
• head: 4ee79131204067f1a74a5f5564cbc9a58abe4ea8

Verification

• focused controlled-send: 5 pass, 0 fail, Ran 5 tests across 1 file. [4.40s]
• sender/log focused suite: 18 pass, 0 fail, Ran 18 tests across 2 files. [4.49s]
• CLI/router contracts: 16 pass, 0 fail, Ran 16 tests across 2 files. [5.74s]
• full matrix before the final test-only vocabulary correction: 4331 pass, 156 skip, with one deployment-axis ratchet failure; affected revalidation after correction: controlled send 5 pass, 0 fail; ratchet 5 pass, 0 fail
• typecheck: review_fix_tsc_1_rc=0
• generated SDK hashes: generated_hash_diff_rc=0
• API/client contracts: 33 pass, 0 fail, Ran 33 tests across 4 files. [2.45s]
• build: build_2_rc=0
• pack: npm_pack_dry_2_rc=0
• no-cloud artifact: emails-package.tgz contains no hosted-control-plane markers (712 text file(s), 12461872 bytes scanned; 0 binary file(s) skipped)
• staged secrets: secrets_staged_3_rc=0; gitleaks_3_rc=0; no leaks found
• independent adversarial review: GO
• commit attribution: exactly one Agent: mamercus; no Co-Authored-By

All fixtures are synthetic. No production mail, real addresses, bodies, attachments, credentials, or external sends were accessed. This PR does not merge, publish, install, deploy, or send email.

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