fix(agent-core-v2): tolerate unresolvable bound model in media registrar refresh

[zicochaos]

Problem

Issue #18 — left over from #16: Agent tool description > renders global tool restrictions in subagent type descriptions (and any session where the bound model alias stops resolving) produced:

[unexpected] Error2: Model "mock-model" is not configured in config.toml.
    at ConfigBackedModelCatalog.getRequester (kosong/model/catalogService.ts:161)
    at AgentMediaToolsRegistrar.refresh (agent/media/mediaToolsRegistrar.ts:102)

AgentMediaToolsRegistrar.refresh runs inside the agent.status.updated listener and called modelCatalog.getRequester(alias) unconditionally. When the bound alias fails to resolve — config edited mid-session, or a stub catalog in tests — the throw happened inside an Emitter listener and was reported as [unexpected]. Tests still passed, so it was pure noise masking real regressions.

What changed

• mediaToolsRegistrar.ts: refresh() now mirrors profileService.tryResolveRawModel — on resolution failure it falls back to no requester (media tools still register, just without a video uploader) instead of throwing inside the listener.
• read-media.test.ts: new case pinning the behavior — binding an unresolvable alias reports no unexpected error and still registers ReadMediaFile. Verified it fails without the fix and passes with it.

Verification

• agent-core-v2: 4231 passed (incl. the new regression test); tool.test.ts 94/94 with zero stderr noise
• oxlint clean on touched files, lint:domain OK, tsc --noEmit clean

Closes #18.