Add relative jog OSC command + Hold on Pause toggle for LTC Out

[chandz102]

Summary

Two small additions to the Generator/LTC Out, both aimed at live
programming workflows (e.g. a lighting programmer jogging back/forward
through a cue while STC drives LTC to a console via Bitfocus Companion):

• /stc/N/gen/jog <seconds> — a new OSC command that performs a
  relative seek (positive = forward, negative = back), reusing the
  existing TimecodeEngine::setGeneratorPosition() /
  getGeneratorCurrentMs() (no engine changes needed — these already
  handle audio-file lockstep seeking and cue-cursor resync correctly).
  Unlike /stc/gen/stop, this preserves Playing/Paused state rather than
  resetting to Start TC, so it behaves like a jog wheel rather than a
  cue-and-restart.
• "Hold on Pause" toggle (LTC Out panel, default off — matches
  current behavior) — when enabled, LTC output keeps encoding the frozen
  timecode instead of going silent while the generator is paused, so
  downstream LTC receivers see continuous signal rather than a dropout
  during a jog/pause. Persisted per-engine like the other LTC Out settings.

Scope

Four files touched, nothing else: MainComponent.cpp, MainComponent.h,
LtcOutput.h, AppSettings.h. Followed existing patterns throughout
(styleOutputToggle, the getBool/settings save-load-per-engine-copy
triplet, the setPaused/isPaused atomic style, Show Lock gating on the
new toggle, etc.) rather than introducing new conventions.

⚠️ Not build-tested

I don't have the Projucer project file or the vendor SDKs (Pro DJ Link,
StageLinQ, BTT) that are gitignored in this repo, so I could not compile
or run this locally. The diff was written and then manually re-verified
line-by-line against the actual source (confirmed every referenced symbol
— btnH, accentPurple, syncing, isShowLocked(), currentEngine(),
both getBool lambdas, etc. — exists and is correctly scoped where used),
but it has not been built or run. Flagging this clearly per your
CONTRIBUTING.md's testing guidance — happy to iterate on anything that
doesn't compile or behave as expected once you're able to build it.

🤖 Drafted with Claude Code + Codex, human-reviewed (source-only, not
build-verified per above).