chore(release): bump instructions to 0.4.21

[andrei-hasna]

Summary

• bump @hasna/instructions from 0.4.20 to 0.4.21
• prepare the already-merged bounded profile compatibility fix for immutable npm release
• change no runtime source or lock metadata

Lineage

• reviewed fix merge: fd0444ed1927111b4d86cafc265027805f6cd6d1 (PR fix: return bounded complete profile reads #61)
• rollout config: 582337eb-f882-4c6e-9206-4979c290eae7
• release task: aa0c8515-234d-4268-ae9a-4db2f48f9854
• remediation task: 898b3895-1f61-4e77-8c52-be28493f1d4a
• rollout task: 54ea58f4-f841-4575-a37f-9498ce3b5d2f

Validation

• bun install --frozen-lockfile --minimum-release-age 604800 — pass
• bun run typecheck — pass
• env -u HASNA_INSTRUCTIONS_API_URL -u HASNA_INSTRUCTIONS_API_KEY -u HASNA_CONFIGS_API_URL -u HASNA_CONFIGS_API_KEY bun test — 621 pass, 0 fail
• bun run build — pass
• npm pack --dry-run --json — @hasna/instructions@0.4.21, 218 files
• staged gitleaks — no leaks found
• committed-head gitleaks — no leaks found

This PR is review-only. Do not merge, tag, publish, install, or apply profiles until the fixed reviewer approves exact head fcc1402eb28765b6f0fa40b2594026eb5bce7289.

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