Revise *.instructions.md: separate AI-relevant special knowledge from background information for contributors (#354)

Revising AI review instructions:
* Reduce context window use for AI review tools, by avoiding repeating common knowledge and API information that is (usually) part of the AI training datasets any way.
* Introduce a mechanism to maintain both parts in single files, to avoid "silent diversion" over time
* Adding a coderabbit path instruction that ensures cross-checking of both parts whenever a PR modifies instruction files

Objectives:
* Primary Goal: only inject content in AI-visible areas that are WLED-MM–specific or which deviate from general knowledge (the context window "token cost" of true false-positive suppressors is always worth it).
* Soft goal: keep each file's AI-facing section lean enough that the signal-to-noise ratio in the attention layer stays high — around 1,500–2,000 words per file type is a reasonable practical ceiling for current models.
* Aspirational: 500 words per file if achievable without sacrificing review quality.

This is an evolution of #353, based on the discussion in https://github.com/MoonModules/WLED-MM/pull/353#issuecomment-4186989873

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

.coderabbit.yaml

@@ -66,3 +66,19 @@ reviews:
         scoped to least privilege. Never interpolate github.event.* values directly
         into run: steps — pass them through an env: variable to prevent script
         injection. Do not use pull_request_target unless fully justified.
+
+    - path: ".github/*.instructions.md"
+      instructions: |
+        This file contains both AI-facing rules and human-only reference sections.
+        Human-only sections are enclosed in `<!-- HUMAN_ONLY_START -->` /
+        `<!-- HUMAN_ONLY_END -->` HTML comment markers and should not be used as
+        actionable review criteria.
+
+        When this file is modified in a PR, perform the following alignment check:
+        1. For each `<!-- HUMAN_ONLY_START --> ... <!-- HUMAN_ONLY_END -->` block,
+           verify that its examples and guidance are consistent with (and do not
+           contradict) the AI-facing rules stated in the same file.
+        2. Flag any HUMAN_ONLY section whose content has drifted from the surrounding
+           AI-facing rules due to edits introduced in this PR.
+        3. If new AI-facing rules were added without updating a related HUMAN_ONLY
+           reference section, note this as a suggestion (not a required fix).