docs(titles): disambiguate the seven colliding page titles (Overview ×3, Bridging ×2, Escrow, Encrypted Payment Comments)

[GigaHierz]

The hole, and the fix

Nine pages shared four titles, so llms.txt (which lists only titles and descriptions) and search results offered an assistant or a reader three pages called "Overview" and two called "Bridging" with no way to tell them apart. This renames seven of them from what the page actually is:

File	was	now
infra-partners/notices/overview.mdx	Overview	Network Notices (its description: active upgrade notices and deprecations)
legacy/overview.mdx	Overview	About Celo L1 (its existing sidebar label)
legacy/validator/key-management/summary.mdx	Overview	Validator Key Management (inbound links already call it "Key Management")
home/bridged-tokens/bridges.mdx	Bridging	Bridging to and from Celo (its own H2; end-user concepts)
tooling/bridges/bridges.mdx	Bridging	Bridge Providers (the page is a list of 11 bridges); description rewritten — the old one had a grammar error and named no provider
legacy/protocol/transaction/escrow.mdx	Escrow	Escrow (Celo L1)
legacy/protocol/transaction/tx-comment-encryption.mdx	Encrypted Payment Comments	Encrypted Payment Comments (Celo L1)

The two current pages (home/protocol/escrow, home/protocol/transactions/tx-comment-encryption) keep their titles; the L1 copies get the suffix. Sidebar labels (sidebarTitle) are unchanged everywhere, so the nav looks the same; only the H1, browser title, search and llms.txt entries change.

What this does NOT do / residual risk

• Does not touch the remaining collision, "Getting Started with Thirdweb" ×2 (build-on-celo/build-with-thirdweb/overview — orphaned — and tooling/dev-environments/thirdweb/overview): task: De-promote thirdweb — keep one tool page at parity with other tools, drop code examples and recommendations #2255 collapses those pages.
• Four of the seven files are under legacy/, which task: Remove the Legacy tab — migrate still-relevant L1 content to Learn/Operate, delete the rest #2254 deletes; the rename is a stopgap for the weeks until then. If task: Remove the Legacy tab — migrate still-relevant L1 content to Learn/Operate, delete the rest #2254 lands first, the legacy hunks disappear in the merge and nothing else needs doing.
• Does not convert the legacy pages' og:description to description (Migrate frontmatter og:description to description on non-legacy pages #2239).
• No URLs change; no redirects needed.

Judgement calls

• Title Case for the new titles, matching every neighbouring page's title (AGENTS.md's sentence-case rule is for headings in the body).
• "(Celo L1)" suffix rather than "Legacy" — it says what the page is about, not where it lives.
• The tooling/bridges description names providers so that an agent picking a page from llms.txt can tell the list from the concepts page. Happy to shorten.

Issues

Refs #2241 — closes 7 of the 9 collisions listed there; the thirdweb pair is left to #2255 (say so when closing).

Stacking / conflicts

Branched off main, independent. Overlaps legacy/* with #2254 (deletes the files — delete wins, no manual resolution) and home/bridged-tokens/bridges.mdx / tooling/bridges/bridges.mdx with #2258 / #2259 (path moves — the title edit carries over in a rename).

Verification evidence

$ # frontmatter titles, all .mdx outside _deprecated/ and snippets/, grouped — collisions remaining:
2 x Getting Started with Thirdweb: build-on-celo/build-with-thirdweb/overview.mdx tooling/dev-environments/thirdweb/overview.mdx
$ git diff --stat
 7 files changed, 8 insertions(+), 8 deletions(-)
$ mint broken-links   # on 9a952cdf
success no broken links found

Before, on main (bdf40b37): Overview ×3, Bridging ×2, Escrow ×2, Encrypted Payment Comments ×2, Getting Started with Thirdweb ×2.

Remaining ops steps

• none

Checklist

• Title is the commit message I want on main
• mint broken-links passes; no nav or URL changes
• Judgement calls flagged above
• No secrets in the diff