feat: add Kimi for Coding provider

[Phototonic]

Summary

• Add Kimi for Coding as a managed API-key usage provider.
• Support one-time OpenCode auth-file prefill, masked/revealable key input, targeted reauthentication, multi-account selection, and ownership-safe refresh requests.
• Add Kimi demo data, QA coverage, an Unreleased changelog entry, and release-facing documentation.
• Ignore local .omo/ and .slim/ plan artifacts without committing their contents.

Validation

• cargo fmt --check
• just check
• cargo test (484 passed)
• appstreamcli validate --no-net resources/app.metainfo.xml
• Live Kimi usage endpoint probe using a locally configured OpenCode credential
• Manual verification of OpenCode prefill and live Kimi usage rendering
• YAPCAP_DEMO=1 cargo run started with Kimi selected and all seven providers ready

Notes

• Package and AppStream release versions remain unchanged; the changelog entry is under Unreleased.