bug(web-ui): require deliberate arming before desktop VFO digit wheel-tuning

[morozsm]

Matching Linear: MOR-1639.

Problem

FrequencyDisplayInteractive.svelte installs an onwheel handler per VFO digit. Unarmed wheel input immediately prevents default scrolling, computes a digit step, and dispatches the frequency change; existing wiring reaches the accumulator and set_freq. Tests intentionally pin immediate unarmed wheel tuning.

During exact-candidate desktop acceptance, a clean direct-frequency submit was followed by a descending burst of frequency writes and the radio moved from 14.281 MHz to 14.230 MHz. Viewport movement was observed and no repeated submit was visible. The runtime event is evidence-consistent with an unintended wheel event, but the exact causal event was not captured and is not proven.

This is a command-safety defect. No TX behavior change is requested.

Acceptance criteria

• An unarmed wheel event over a VFO digit produces zero frequency callbacks and zero set_freq operations, and does not prevent page scrolling.
• After an explicit deliberate activation/arming gesture, each wheel gesture produces exactly one digit-appropriate frequency step.
• Preserve click-plus-Arrow keyboard operation.
• Do not change burst accumulator or rate-limiter semantics.
• Add regression witnesses at primitive, VfoSurface/wiring, and conformance levels.
• No TX behavior changes.

Relationships

Relates to MOR-1410 / Core #2318. Relates to historical MOR-1322 and MOR-1425; do not reopen or close those issues.

Scope

Public RigPlane Core web UI only.