Publish hardware-tested firmware v0.4.2 beta

[yyods]

Summary

• reconcile public main with the exact source lineage used to build and deploy firmware v0.4.2
• publish the supplemental production-browser validation record for ESP32 4 MB and ESP32-S3 N16R8
• expose immutable firmware hashes and release evidence from the website
• align README, specifications, product documentation, and publication guards with the accurate hardware-tested beta, not formally qualified posture
• keep ESP32-C3 unavailable until its exact profile is tested

Provenance

This branch deliberately retains the tested release source ce02b68ab73da903035aa9f992c1f7e8eb2a3691 and the currently deployed website source 88b649c03c8ba80135c617332b4c3b6b028a8f60 in ancestry. The reconciliation merge uses the tested tree because the four public-main-only commits describe an older pre-activation state that the completed browser validation superseded.

After required checks pass, this PR must be merged with a provenance-preserving merge commit. Rebasing or squashing would rewrite or sever the already-tested release lineage.

Validation

• Flutter dependency lock, localization generation, formatting, analysis: pass
• Flutter non-golden tests: 628 passed
• Website formatting, lint, typecheck, license gate, unit tests, and static builds: pass
• Website tests: 174 passed
• Deployment smoke now requires GET and HEAD 404/no-store responses for the retired v0.4.1 candidate and unversioned social cards
• Publication, documentation-link, no-leak, SPDX, import-boundary, locale, patch-policy, and DCO gates: pass
• Firmware aggregate host suite against pinned MicroPython e0e9fbb17ed6fd06bb76e266ae554784c9c80804: 23 test files, 0 failures
• Audited v0.4.2 candidate validation and archive verification: pass
• Exact browser erase/install and interrupted-flash recovery: pass on ESP32 4 MB and ESP32-S3 N16R8
• Live retired v0.4.1 descriptor/manifest GET and HEAD checks: 404 with Cache-Control: no-store

Release posture

Firmware v0.4.2 remains a beta. The two exact profiles above have passed the documented browser install/recovery scope; the broader formal qualification matrix remains pending.