debt(web-ui): acknowledge desktop direct-frequency submission

[morozsm]

Matching Linear: MOR-1640.

Problem

The desktop direct-frequency field has a local draft and dispatches only on Enter or Set. After commit, the input remains focused and populated; its hint is only a pre-submit interpretation. There is no local accessible submitted, pending, confirmed, or error state, and the Set control has no state or label change.

This ambiguity led to two Enter submissions for the same target in an earlier attempt, six seconds apart. Owner ruling: this feedback polish is non-blocking backlog work and must not by itself block MOR-1410.

Acceptance criteria

• Enter and Set expose clear, accessible submitted, pending, confirmed, and failure states without treating transport acceptance as radio confirmation.
• Prevent accidental duplicate same-target submit while pending.
• Preserve the draft input while clearly distinguishing it from canonical radio state.
• Add tests for Enter, Set, duplicate-pending prevention, confirmed/failure feedback, and accessible status.

Relationships

Relates to MOR-1410 / Core #2318 and MOR-1441. This UX debt is non-blocking and must not, by itself, block MOR-1410.

Scope

Public RigPlane Core web UI only.