story: Operate tab — move infra-partners/* to operate/* and fold Specs in as a Specification section

[GigaHierz]

Part of #2266.

User story

As a node operator, RPC provider, exchange or custodian, I want one tab with run-a-node, notices and the protocol specification — instead of "Infra Partners" and "Specs" as two separate tabs.

Context & evidence

At bdf40b37: "Infra Partners" (docs.json:405) has 22 pages — infra-partners/notices/ (overview, op-geth-deprecation, req-resp-cl-sync-deprecation, plus archive/ with 7 past notices) and infra-partners/operators/ (12 pages: architecture, archive-node, configuration, historical-proofs, maintenance, migrate-node, monitoring, network-config, overview, public-rpc-node, run-node, troubleshooting). "Specs" (docs.json:457) has 16 pages under specs/ (index, deployments, l1-smart-contract-verification, token-duality, transaction-fees, fee-abstraction, transaction-types, native-bridge, eigenda, finality, l2-migration, smart-contract-updates-from-l1, upgrades/{jovian,jello,ice-cream,isthmus}).

Decided: Specs lives under Operate as a "Specification" section, with redirects from the old specs paths.

The #2209 Appendix A Operate section is stale — its "Integration" group lists 6 infra-partners/integration/* files that do not exist on main, and its notices list predates the archive split. Re-derive the mapping from infra-partners/ at bdf40b37 before starting.

Scope

• Rename Infra Partners → Operate; move infra-partners/* → operate/* keeping the current groups (Network Notices current + archive / Node Operation / Node Management / Reference)
• specs/* → operate/specification/* (Specification + Deployments; Protocol Upgrades + L2 Migration)
• Fold tooling/nodes/run-a-celo-node into the run-node page
• Include whatever task: Remove the Legacy tab — migrate still-relevant L1 content to Learn/Operate, delete the rest #2254 classified as "keep → Operate"
• Redirects: /infra-partners/:slug* → /operate/:slug*, /specs/:slug* → /operate/specification/:slug*, plus the old specs.celo.org path mapping — coordinate with the celo-org/specs redirect-stub work referenced in Deduplicate migrated Specs pages against the Home and Build guides #2227 so heading fragments survive

Acceptance criteria

• Tab renamed; Specs tab removed
• All 22 + 16 pages reachable from nav
• Redirects verified, including 5 sampled specs.celo.org-era URLs with fragments
• .github/CODEOWNERS lines for /infra-partners/ and /specs/ updated to the new paths
• npx mintlify broken-links + orphan check green

Non-goals

Editing spec content (#2227); Legacy classification (#2254).

Depends on / blocks

Depends on #2252, #2254. Blocks #2261.

Measured at: bdf40b37