docs(db): rename gittensory prose to loopover in migration headers

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Summary

• Part of the gittensory→loopover rebrand (Epic: complete the gittensory -> loopover rebrand (full cutover, no dual-support) #5705), phase 8b: rename brand-name prose in the comment-only -- headers of 35 migration files. DDL itself is untouched, including the two 'gittensory-native' source column DEFAULT clauses in 0049_review_audit_parity.sql and 0126_contributor_gate_history.sql — a real review_audit/contributor_gate_history provenance discriminator value that other code compares against exactly, not prose.

Scope

• The PR title follows type(scope): short summary Conventional Commit format.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• I linked a currently open issue this PR resolves — N/A, maintainer-authored rebrand-epic cleanup (Epic: complete the gittensory -> loopover rebrand (full cutover, no dual-support) #5705), no linked-issue gate applies to owner PRs.

Validation

• git diff --check
• npm run db:migrations:check — 152 migrations OK, contiguous, no new duplicates
• npm run db:schema-drift:check — schema.ts matches migrations/

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed.
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics.
• Auth, cookie, CORS, GitHub App, Cloudflare, or session changes include negative-path tests. — N/A, no such changes.
• API/OpenAPI/MCP behavior is updated and tested where needed. — N/A, comment-only, no schema change.
• UI changes use live API data or real empty/error/loading states. — N/A, no UI changes.
• Visible UI changes include a UI Evidence section. — N/A, no UI changes.
• Public docs/changelogs are updated where needed; changelogs are only edited for release-prep PRs (none touched here).

Notes

• Final batch of the bulk-prose portion of rebrand epic Epic: complete the gittensory -> loopover rebrand (full cutover, no dual-support) #5705.

[superagent-security]

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