fix(asusd): carry Slash display mode as u8 over the D-Bus stack

[NB-Group]

Split out of #230, where it was buried inside the UI redesign. It is a self-contained backend change and has nothing to do with the UI work, so it gets its own PR.

The Slash display mode was leaking through the D-Bus stack as the raw animation interval, while every caller actually wanted the mode discriminant. Thread it as u8 instead:

• rog-slash: SlashMode is now #[repr(u8)]
• asusd trait impl + rog-dbus binding return u8
• asusctl CLI parses u8
• rog-control-center setup_slash consumes u8, with a short retry because the single post-startup read races asusd coming up

No UI page is touched. Builds clean across rog-slash / rog-dbus / asusd / asusctl / rog-control-center.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Corrected the reported Slash display mode so it reflects the configured mode rather than the display interval.
  • Improved Slash mode loading and updates with validation, including a retry when initial loading fails.
  • Unknown or invalid mode values now produce a warning and preserve a safe default instead of causing failures.
  • CLI output now displays recognized mode names and clearly identifies unrecognized values.

Walkthrough

Slash mode access now uses raw u8 values at the D-Bus boundary. Consumers validate those values with SlashMode::try_from, retry failed UI reads, and report unknown modes without applying invalid state.

Changes

Slash mode validation

Layer / File(s)	Summary
SlashMode byte contract rog-slash/src/data.rs	SlashMode now has an explicit u8 representation. TryFrom<u8> maps known discriminants and rejects unknown values.
D-Bus mode access rog-dbus/src/zbus_slash.rs, asusd/src/aura_slash/trait_impls.rs	The D-Bus getter returns the raw configured display mode byte. The asusd getter returns display_mode instead of display_interval.
UI and CLI mode handling rog-control-center/src/ui/setup_slash.rs, asusctl/src/slash_cli.rs	The control center validates startup and event values, retries failed reads once, and keeps its default mode after repeated failure. The CLI displays validated names or an unknown(0x..) fallback.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• OpenGamingCollective/asusctl#211: Extends the Slash refactor with related SlashMode, D-Bus, UI, and CLI changes.
• OpenGamingCollective/asusctl#240: Relocates Slash mode handling across related modules.
• OpenGamingCollective/asusctl#238: Also modifies the Slash CLI handlers and connection handling.

Suggested labels: asusd, asusctl, rog-slash, rog-control-center, fix

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description clearly summarizes the change, motivation, scope, and claimed build status, but it omits the required template sections and verification checklist.	Add the required Description, issue, Tested Hardware & Environment, and Verification and testing sections, then mark each completed verification item.

✅ Passed checks (3 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly describes the primary change: carrying the Slash display mode as u8 through the asusd D-Bus stack.

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