fix(release): auto-derive .release-please-manifest.json instead of hand-editing it

[JSONbored]

Summary

#7100 fixed the immediate .release-please-manifest.json mismatch by hand-typing corrected version numbers -- exactly the failure mode that caused the drift in the first place (a human-authored value instead of one derived from source of truth). This replaces that with a real mechanism, so it's a one-command fix from here on, never a manual edit:

• scripts/sync-release-manifest.mjs treats each package's own package.json "version" as authoritative and syncs the manifest to match. npm run release-manifest:sync is now the supported way to fix drift.
• npm run release-manifest:sync:check -- wired into both test:ci and .github/workflows/ci.yml (gated on backend/mcp/engine/miner/ui) -- fails CI the moment the manifest and a package's package.json disagree, instead of surfacing days later as release-please re-proposing an already-published version as a brand-new Release PR (what happened with chore(release): cut miner v3.1.1 #7086/chore(release): cut mcp v3.1.1 #7087).
• .release-please-manifest.json and release-please-config.json are now part of the backend path filter, so an edit to either alone still triggers the check.

Also corrects reference.md's CI check table, which still claimed manifest:drift-check/engine-parity:drift-check weren't wired into ci.yml -- stale since #7067 actually added them -- and adds table rows for all 5 checks that landed across #7067 and this PR.

Test plan

• npm run actionlint -- clean
• npx vitest run test/unit/sync-release-manifest.test.ts -- 8/8 pass (pure-function + injected-io coverage mirroring sync-release-lockfile-versions.test.ts's established pattern)
• npm run typecheck -- clean (after npm run build --workspace @loopover/engine)
• npm run release-manifest:sync:check -- passes against the real, already-correct manifest; manually verified it fails loudly when a version is hand-corrupted, then re-passes after npm run release-manifest:sync
• npm run docs:drift-check -- clean

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.75%. Comparing base (ead6fdd) to head (1b42787).
⚠️ Report is 7 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7102   +/-   ##
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  Coverage   93.75%   93.75%           
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  Files         692      692           
  Lines       68808    68808           
  Branches    18781    18781           
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  Hits        64511    64511           
  Misses       3302     3302           
  Partials      995      995           

Flag	Coverage Δ
rees	88.56% <ø> (ø)
shard-1	43.78% <ø> (+0.44%)	⬆️
shard-2	36.84% <ø> (-0.06%)	⬇️
shard-3	33.14% <ø> (-0.03%)	⬇️
shard-4	34.47% <ø> (+0.08%)	⬆️
shard-5	32.29% <ø> (+0.61%)	⬆️
shard-6	45.76% <ø> (-0.32%)	⬇️

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