fix: resolve pre-existing broken anchors and missing attachments in reference docs

[marc0olo]

Summary

Pre-existing issues found during review of PR #188 (ic-interface-spec split). None were introduced by that PR.

Quick wins — broken anchors (one PR)

File	Issue
docs/references/ic-interface-spec/canister-interface.md	#ic-vetkd_encrypted_key anchor — method was renamed in portal source
docs/references/ic-interface-spec/management-canister.md	ic_ vs ic- typo in 3 anchor links
docs/guides/digital-assets/chain-key-tokens.mdx	Broken same-page anchors
docs/guides/authentication/verifiable-credentials.md	Broken same-page anchors
docs/references/candid-spec.md	Broken same-page anchors
docs/references/glossary.md	Broken same-page anchors

Needs investigation

File	Issue
docs/getting-started/project-structure.mdx	2 links to non-existent binding-generation.md — find where that content lives now

Won't fix (upstream decision needed)

Missing _attachments/ files referenced in the IC interface spec: certificates.cddl, requests.cddl, http-gateway.did. These were never served on this site; links are inherited from the portal source. Needs decision on whether to host them or remove the links.

Notes

• Cross-reference the anchor-to-file mapping comment at the bottom of docs/references/ic-interface-spec/canister-interface.md when fixing the vetkd anchor
• Run grep -rn "binding-generation" docs/ to find all references before fixing project-structure.mdx

[marc0olo]

All broken anchor items from this issue are addressed in PR #195. Here's the mapping:

Item	Fix
canister-interface.md — #ic-vetkd_encrypted_key	→ ./management-canister.md#ic-vetkd_derive_key (method was renamed in portal source)
management-canister.md — ic_ vs ic- typo (×3)	→ #ic-upload_canister_snapshot_metadata (all 3 occurrences)
chain-key-tokens.mdx — broken #canister-ids same-page anchor	→ ../../references/chain-key-canister-ids.md (section was moved to a separate page)
verifiable-credentials.md — broken #requesting-a-credential	→ #implementing-a-relying-party
candid-spec.md — stale portal anchors (×4)	→ #the-did-file and #safe-interface-upgrades
glossary.md — "broken same-page anchors"	All 47 same-page anchors in the file resolve correctly. The actual issue was references/cycles-costs.md linking to glossary.md without #xdr — fixed.
project-structure.mdx — 2 links to non-existent binding-generation.md	→ candid.md#binding-generation

The missing attachments (certificates.cddl, requests.cddl, http-gateway.did) are not covered — those need a separate decision as noted in the issue.