perf: update the menu bar angle only when needed

[Jah-yee]

Problem

StatusItemController ran a 250 ms timer for its entire lifetime, even when Show angle in menu bar was off (the default). Most timer firings therefore read the angle and touched no UI.

Change

• observe the visibility preference instead of polling it
• subscribe to angle changes only while the title is enabled
• format and de-duplicate whole-degree titles before writing AppKit state
• preserve the previous 4 Hz update ceiling with a latest-value throttle
• publish the initial title immediately, then cancel and clear it immediately when disabled

The lid sensor's own polling is unchanged; this only removes hidden status-title wakeups and redundant title assignments.

Edge cases

• the persisted enabled state produces a title during controller initialization
• repeated on/off toggles replace, rather than accumulate, subscriptions
• cancellation drops any throttled trailing value before the title is cleared
• weak captures and explicit cancellation avoid retaining the status controller

Validation

• debug build with Swift warnings treated as errors
• release build with Swift warnings treated as errors
• git diff --check
• verified clean automatic merges with PRs Fall back to blit mipmaps when the MPS pyramid encode fails #8, fix: use the built-in lid sensor #11, ci: validate pull request builds #14, fix: apply Live rendering changes during active effects #15, and fix: fail closed when capture filters are unsafe #16
• PRs Add automatic mode #6 and Fix overlay getting stuck when start angle is high #9 already conflict with current main; this change adds no overlapping files
• verified with a small Combine timing harness that the explicit initial write is needed and cancellation suppresses a queued latest value