Add backward-compatible structured proposal metadata across all surfaces

[egekoca]

Summary

• define and document a deterministic STOLLA_PROPOSAL_METADATA_V1 envelope inside the existing Governor description string
• add strict Unicode-aware field and UTF-8 envelope bounds, HTTPS-only discussion links, and safe legacy fallback parsing
• replace the free-text creation textarea with title, summary, body, discussion link, field validation, counters, and live preview
• render structured title/summary/body across global and community list/detail surfaces while preserving legacy plain text
• map parsed metadata through the shared proposal event/discovery pipeline and cover both legacy and versioned fixtures
• repair inherited Consolidate proposal and Governor event modules into one pipeline #256 workspace lock/test/E2E inconsistencies so this branch is independently verifiable against main

The branch includes the event-pipeline commit required by #256, so this PR is self-contained even while #278 remains open. If #278 lands first, GitHub will naturally remove that already-merged commit from this diff.

Security and compatibility

• no Governor contract, transaction payload, or proposal-ID changes
• malformed/unknown envelopes render as inert legacy text
• discussion links require absolute HTTPS without credentials and render with noopener noreferrer plus no-referrer policy
• E2E fixture flags fail closed in production

Verification

• npm run test:web — 460/460 passed
• node --test scripts/check-production-health.test.mjs — 6/6 passed
• npm run test:e2e:ci — 30/30 desktop + mobile passed
• npm run lint
• npm run typecheck
• npm run build
• npm run check:workspace
• git diff --check

Closes #255

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