Add deterministic guards for mechanical CRDT follower invariants

The CRDT follower review profile currently delegates several repeatable syntax/import checks to LLM inference on every relevant diff. At `origin/main@5882b01388fd2d5ef72e00f92e7761ef5f91f3d8`, the strongest deterministic candidates are `.agents/checks/follower-boundary.md:31-33`, `:62-72`, and `:82-93`: outbound `update_b64` construction, mint/applier imports at retry boundaries, distribution conditionals inside follower core, hardcoded endpoint literals, and branch-pinned catalog references. The repo has no follower-specific ESLint, Semgrep, or import-graph rule covering these patterns.

Extract that mechanical subset into path-scoped ESLint AST selectors, Semgrep, and/or an import-graph script wired to CI. Keep the profile for semantic review: distinguishing shared from local docs until capabilities are branded, indirect writer/applier behavior, layout/presence/overlay intent, unified-auth correctness, and deciding where runtime assertions are warranted. PRs [#16373](https://github.com/Comfy-Org/ComfyUI_frontend/pull/16373), [#16375](https://github.com/Comfy-Org/ComfyUI_frontend/pull/16375), [#16396](https://github.com/Comfy-Org/ComfyUI_frontend/pull/16396), and [#16432](https://github.com/Comfy-Org/ComfyUI_frontend/pull/16432) do not add this guard; [#16373](https://github.com/Comfy-Org/ComfyUI_frontend/pull/16373) strengthens retry identity at runtime but does not replace the repeated inference check.

```text
[PR diff: agent follower seam]
|
v
[Deterministic guard layer]---->[syntax/import violation: CI fails]
| clean
v
[LLM semantic remainder]------->[shared-vs-local doc, indirect writer, intent]
```

Category: Code Pattern Matching (4). Confidence: medium-high. Freshness checked at `5882b01388fd2d5ef72e00f92e7761ef5f91f3d8`; independently verified by a second audit pass. Filed from OPP-53 using the determinism-audit rubric.