fix: fixed fan control helper on M5

[c-herz]

Fan control is broken on M5 gen. Setting mode or speed through the UI or smc CLI does nothing, even though RPM reads work fine.

Two issues: M5 uses F%dmd (lowercase) for the fan mode key instead of F%dMd, and the uppercase key doesn't exist so writes are silently ignored. Second, Ftst doesn't exist on M5, but unlockFanControl bails out immediately if it can't read Ftst.

Changes:

• Added fanModeKey() on SMC that probes F0md once and caches the result, returning the correct key name per platform (Intel always gets uppercase at compile time).
• Restructured unlockFanControl to try a direct mode key write first (which is all M5 needs), then fall back to the Ftst unlock mechanism for M1-M4.
• resetFanControl similarly handles missing Ftst by resetting each fan's mode key directly.
• Extended the getValue zero-byte exemption list with the lowercase variants (F0md, F1md).
• Replaced all hardcoded F%dMd references across smc.swift, readers.swift, and main.swift with fanModeKey().

Tested on MacBook Pro 14" M5 Pro (15-core CPU): manual mode, speed control, and reset all work correctly through both the CLI and the Stats UI. Would appreciate confirmation on base M5, M5 Max, and M1-M4 to make sure nothing regressed.

[exelban]

can confirm that it works fine for m1