Encapsulate led.cpp's own runtime state as static, not global

[netmindz]

Summary

Part of an ongoing pass identifying WLED_GLOBAL declarations that are actually only referenced in one file (see #5777, #5778 for earlier ones). 5 more turned out to be private to led.cpp: briNlT, colNlT, lastNlUpdate, transitionActive, transitionStartTime.

Converted all 5 to file-local static, same types and initial values as before.

No behavior change — purely a storage-class change.

Test plan

• esp32dev: builds and links cleanly via pio run -e esp32dev — 1,320,323 bytes flash, no warnings.
• Confirmed via repo-wide grep (wled00/, usermods/) that none of the 5 converted variables are referenced outside led.cpp.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor
  • Improved internal handling of transition and nightlight runtime state.
  • No user-facing behavior or configuration changes.

[coderabbitai]

Walkthrough

The change moves transition and nightlight runtime state from wled.h into file-private variables in led.cpp. Transition configuration globals remain declared in wled.h.

Changes

LED runtime state

Layer / File(s)	Summary
Private runtime state wled00/wled.h, wled00/led.cpp	led.cpp now owns file-private transition and nightlight runtime variables. wled.h retains only transition configuration globals and documents the private state.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• wled/WLED#5777: Encapsulates file-specific runtime state by moving globals from wled.h into implementation files.

Suggested labels: minor

Suggested reviewers: dedehai, softhack007

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes converting led.cpp runtime state from global to file-local static variables.

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[DedeHai]

this will conflict my PR #5700 but not a big deal.