feat(mediainfo): declare snapshot v2 APIs

[SuperMonster003]

Summary

• add the AutoJs6 MediaInfo declaration module
• declare snapshot schema constants, strict v1/v2 overloads, capabilities, and the dynamic v2 track envelope
• register the declaration from declarations/autojs6/index.d.ts
• add a focused overload smoke test

Narrow integration

The remote baseline predates the MediaInfo declaration. This PR adds only the MediaInfo declaration, one index reference, and one focused smoke file. It does not include unrelated generated Android resources, Pinyin declarations, or the broader local declaration history.

Coordination

• Plugin contract and implementation: feat: add opt-in snapshot v2 contract AutoJs6-Plugin-MediaInfo#3
• Host schema negotiation and Rhino/Node bridge: https://github.com/SuperMonster003/AutoJs6-Private/pull/4
• Node Runtime facade: feat(mediainfo): expose snapshot v2 negotiation AutoJs6-Plugin-NodeJs-Runtime#1
• API documentation: docs(mediainfo): document snapshot v2 negotiation AutoJs6-Documentation#15
• TypeScript declarations: feat(mediainfo): declare snapshot v2 APIs #8

All five pull requests remain Draft and should be reviewed as one coordinated contract set. None of them changes a release version or authorizes a merge/release.

Validation

The new declaration and focused overload smoke pass TypeScript checking with noResolve and skipLibCheck disabled. The full old baseline is not a usable modern-tsc gate because its existing generated Android and Java declarations contain reserved-word syntax errors; those pre-existing files are unchanged by this PR.

Not included

• generated Android resource refresh
• unrelated declaration modules
• version bump or publication