docs: remove the Legacy tab

[palango]

The Legacy tab mixed three kinds of content: dead L1 documentation, current pages that were misfiled there (the Cel2 FAQ, the native-bridge guides, account metadata), and the only concept docs for staking mechanisms that still run on L2. This removes the tab and sorts its 60 pages: 13 move to where they belong, 2 fold into a new About Celo L1 history page, and 45 are deleted with a redirect to the live page that answers the same question. It follows the redirect standard from #2279: every destination is a final, in-nav page, and the 109 pre-existing redirects that pointed into legacy/ are re-pointed to the same targets. Closes #2254.

Changes

New and moved pages:

• home/celo-l1 distills legacy/overview and legacy/l1-architecture: L1 history, the L1-vs-L2 comparison table, and one-line summaries of every retired mechanism, so the historical redirects land somewhere that explains what the reader was looking for.
• A new Staking group under Home holds the still-operational PoS docs: locked-celo, validator-elections, validator-groups, voting, and the three key-management pages. Stale L1 claims (BFT consensus, block production, consensus-signer restrictions) are stripped; elections are described via the EpochManager flow the specs and community-RPC pages document.
• home/protocol/metadata (from legacy/protocol/identity/metadata): the claims mechanism is what community RPC URL registration uses today, so it is live content, not identity history.
• infra-partners/operators/faq (from legacy/faq): a current operator FAQ that was only legacy by filing accident. The site-wide FAQs anchor follows it.
• home/bridged-tokens/bridging-celo-from-ethereum and home/bridged-tokens/withdrawing-celo-to-ethereum (from legacy/transition/guides/): the native bridge is a permanent L2 feature, not migration history. Both guides carried addresses from a retired testnet deployment; they now use the current Celo Sepolia CeloTokenProxy and OptimismPortalProxy from tooling/contracts/l1-contracts.

Deletions: 45 pages, each diffed against its live counterpart before deleting. The full path-by-path mapping is in the classification comment on #2254. Ported during the diff pass: the Registry/GoldToken lookup into home/protocol/celo-token, the keystore-extraction tip into infra-partners/operators/migrate-node, and the MaxCodeSize change into specs/l2-migration.

Redirects: 60 new /legacy/* entries, 128 existing destinations re-pointed, the /what-is-celo/about-celo-l1/:slug* wildcard now lands on /home/celo-l1, and about 30 content links into legacy/* fixed.

Facts checked on chain while editing: the bridge addresses (eth_getCode on Ethereum Sepolia; the old guide addresses have no code behind them), Election.maxNumGroupsVotedFor = 10 (the moved locked-CELO page said 3), and proofMaturityDelaySeconds = 604800 on the Celo Sepolia portal (the withdrawal guide claimed finalization takes about 2 minutes; it takes 7 days).

Verification

$ npx mintlify broken-links
success no broken links found

$ bash scripts/check-orphans.sh
Found 23 orphan page(s): .mdx files not referenced in docs.json navigation

The orphan set is the base branch's 25 minus the two legacy pages that were themselves orphaned; no page added here is orphaned. A redirect audit over all 692 entries confirms every destination resolves to a page on disk, is listed in navigation, and is not itself a redirect source. Anchors used in redirects and re-pointed links were checked by hand, since the link checker ignores anchors.

Not verified: the two bridge code examples were not executed end to end (that needs a funded Sepolia account holding CELO); their addresses and the challenge period were verified on chain instead.

Flags

• identity/odis-use-case-key-hardening and identity/encrypted-cloud-backup had no live equivalent. Deleting them assumes no current wallet still uses ODIS key hardening or PEAR backup; speak up before merge if that is wrong.
• The identity redirects point at tooling/libraries-sdks/contractkit/odis because the canonical SocialConnect page is one of the 23 known orphans, and orphans cannot be redirect targets. When task: Orphaned-pages audit — re-nav or delete the 22 pages on disk that are missing from navigation #2253 adds it to navigation, these can be tightened.