clampVadField throws TypeError on unknown keys and resolveContextSileroEnabled misses mixed-case contexts

[hsusul]

Describe the bug

In src/helpers/whisperVadConfig.js:

1. clampVadField(key, value) unconditionally accesses LIMITS[key]:
   const { min, max, round } = LIMITS[key];
   When an unlisted/extra key is passed (or DEFAULTS has a property not present in LIMITS), it throws:
   TypeError: Cannot destructure property 'min' of 'LIMITS[key]' as it is undefined.
2. resolveContextSileroEnabled(settings, context) performs strict string comparisons against "dictation", "noteRecording", and "meeting". If the context string has surrounding whitespace or uppercase casing (e.g., "DICTATION" or " NoteRecording "), it skips the proper branch and falls through to true.

To Reproduce

1. Call clampVadField("customOption", 10) -> throws TypeError.
2. Call resolveContextSileroEnabled({}, "DICTATION") -> returns true (expected false for dictation).

Expected Behavior

• clampVadField should safely return the value or fallback if no limit definition exists.
• resolveContextSileroEnabled should normalize the context parameter.

[gabrielste1n]

Closing with #1926 — full end-to-end trace there: the described failure shape isn't reachable from any production call site.