feat(server): Resolve built-in agent persona routes

[bryantderosier]

What does this implement or fix?

Resolves each persona's ordered primary and fallback model targets against environment provider snapshots with typed rejection reasons and no implicit third fallback.

This is PR 3 of 10 in GitHub stack pingdotgg#120. It targets feature/agent-persona-catalog and depends on #76.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (clean-up or code structure improvement without changing behavior)
• Documentation update

How has this been tested?

vp test run apps/server/src/j5/agents/agentPersonaRouting.test.ts — 5 tests passed.

The combined local integration suite also passed 350 tests across 17 files, scoped typechecks for server, web, mobile, contracts, and client runtime, and lint for 54 changed TypeScript files.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots or GIFs (Optional)

Not applicable.

Merge order

This PR is part of GitHub stack pingdotgg#120. Merge from bottom to top:

#75 -> #76 -> #78 -> #79 -> #80 -> #81 -> #83 -> #82 -> #85 -> #118

Stack rebuilt 2026-09-09 (stack pingdotgg#120): #84 and #86 were dropped, and fork-boundary refactors moved the persona RPCs, guards, and client wiring into J5-owned files. Review threads were preserved.

Generated with GPT-5 using the Codex desktop app.

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