fix: warn when effect registration exceeds the list limit

[keeltrace]

Fixes #5827.

When WS2812FX::addEffect() reaches the 254-effect capacity, it currently returns 255 silently. Most usermods discard that return value, so dropped effects are difficult to diagnose.

This adds a debug warning only on the full-list failure path and includes the effect metadata string that could not be registered. It intentionally does not change the 8-bit effect ID limit or overlap with the separate larger-effect-ID work.

Validation:

• git diff --check
• reviewed against current main

I could not run a firmware build locally because PlatformIO is not installed in this environment.

Summary by CodeRabbit

• Bug Fixes
  • Added diagnostic messages when the effect list reaches its maximum capacity, including a warning and the affected effect name.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Team

Run ID: 4c100c7f-f5d8-4b96-887e-7f6665026470

📥 Commits

Reviewing files that changed from the base of the PR and between 92064ae and b4567b7.

📒 Files selected for processing (1)

• wled00/FX.cpp

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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Walkthrough

WS2812FX::addEffect now logs a warning and the rejected effect name when the effect list is full before returning 255.

Changes

Effect List Diagnostics

Layer / File(s)	Summary
Log rejected effects wled00/FX.cpp	The full-list failure path logs that the effect list is full and prints the effect name before returning 255.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to b4567

When the effect list is full, rejected effects now produce a debug warning with their metadata while retaining existing registration behavior. No current merge-blocking risk remains.

Suggested reviewers: dedehai

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the added warning for effect registration attempts beyond the list limit.
Linked Issues check	✅ Passed	The change satisfies issue #5827 by adding debug output when the effect list is full, including the dropped effect name, while preserving the existing effect-count limit.
Out of Scope Changes check	✅ Passed	The changes are limited to diagnostic output in the full-list failure path and do not introduce unrelated behavior or scope.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.

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