Support unlimited named API-key provider instances

[TheGreatAxios]

Summary

• First-class API-key providers now name an instance before the key (same multi-instance model as OAuth accounts).
• Instances store as kind/slug catalog rows so a second key cannot silently overwrite the first; reusing a name confirms before replace.
• Alt+A account counts include API-key instances; Custom remains free-form.

Closes CL-5898.

Verification

• bun run typecheck
• bun run build
• bun run test (4541 pass, 0 fail)

Notes

• Legacy bare keys (e.g. openai) still count as the default slug and are updated in place on confirmed reconnect.

[linear-code]

CL-5898

[TheGreatAxios]

Critique

Lens: behavioral correctness and multi-instance safety
Verdict: approve
Summary: First-class API-key connects name instances before the key and store kind/slug catalog rows so a second key cannot overwrite the first; confirmed reuse updates in place, including legacy bare keys.

Findings: none.

Greybeard

Lens: architecture and documentation alignment
Verdict: approve
Summary: Reuses the OAuth multi-instance slug machinery (oauthProfile, suggest/confirm) for API-key kinds without pulling Custom into that path; PRODUCT/TUI/CHANGELOG describe the shipped behavior.

Findings: none.

gaasbot

Lens: public OSS / release readiness
Verdict: approve
Summary: UX, tests, and docs are contributor-readable; no secrets, machine paths, or private assumptions land in the tree.

Findings: none.