Promote externally-consumed agent paths into the public API surface

[jorgeraad]

A few specialized-agent paths under src/core/agents/specialized/ are entry points for external consumers but aren't exposed through the package's public API (src/core/api/index.ts). Today they exist as compatibility shims pinned in place by deep imports.

Files involved:

• src/core/agents/specialized/authenticationAgent/index.ts
• src/core/agents/specialized/environment/index.ts
• src/core/agents/specialized/patching/index.ts
• src/core/agents/specialized/codeAgent/schemas.ts

The deep-import path means changes to apex's internal layout can break external builds, and the files have to be carved out of dead-code detection by listing them as entry in knip.json. Cleanest fix:

1. Re-export the symbols those files expose through src/core/api/index.ts (or a similar curated surface).
2. Migrate external consumers to import from @pensar/apex instead of @pensar/apex/src/core/agents/specialized/<x>.
3. Drop the four compatibility files and their knip.json entries.

This is bookkeeping rather than urgent — current state works. Tracked here so the path forward is explicit when someone has cycles.