refactor: delete orphaned per-provider caching transform files

[hannesrudolph]

Summary

Deletes 4 orphaned source files and 4 orphaned test files from src/api/transform/caching/. These addCacheBreakpoints() functions have zero provider consumers — no provider file imports them.

Cache breakpoint placement has moved to inline providerOptions in each provider's createMessage() method:

• Anthropic/Anthropic Vertex/Minimax: { anthropic: { cacheControl: { type: "ephemeral" } } } via applyCacheControlToAiSdkMessages()
• Bedrock: { bedrock: { cachePoint: { type: "default" } } } via applyCacheControlToAiSdkMessages()
• Gemini/Vertex: No breakpoints set (server-side auto-caching)

Files Deleted

File	Lines	Former Strategy
caching/anthropic.ts	41	system + last 2 user (OpenAI-format input)
caching/gemini.ts	47	system + every Nth user (frequency-based)
caching/vertex.ts	49	last 2 user (Anthropic-format input)
caching/vercel-ai-gateway.ts	30	system + last 2 user
caching/__tests__/anthropic.spec.ts	—	Tests for above
caching/__tests__/gemini.spec.ts	—	Tests for above
caching/__tests__/vertex.spec.ts	—	Tests for above
caching/__tests__/vercel-ai-gateway.spec.ts	—	Tests for above

Total: 1,025 lines deleted.

Verification

• Confirmed zero imports of addCacheBreakpoints or from.*caching/ across all provider files
• All 5,499 tests pass
• Lint and type checks clean

---

Important

Removed the entire caching module including all provider-specific implementations and their test files for the addCacheBreakpoints functionality.

• Deleted caching implementations:
  • Removed anthropic.ts, gemini.ts, vercel-ai-gateway.ts, and vertex.ts files containing provider-specific addCacheBreakpoints functions.
• Deleted test files:
  • Removed anthropic.spec.ts, gemini.spec.ts, vercel-ai-gateway.spec.ts, and vertex.spec.ts test files covering the caching functionality across all providers.

^{This description was created by for 2c4f10a. You can customize this summary. It will automatically update as commits are pushed.}

[roomote]

Rooviewer   See task

No issues found. The 8 deleted files are confirmed orphaned -- zero imports of addCacheBreakpoints or any caching/ module exist across the codebase. The replacement (applyCacheControlToAiSdkMessages) is already in place in the relevant providers.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}