* Add v-development skill
Teach Copilot V language development: toolchain, v.mod layout, build/test/fmt, and Option/Result error handling.
* Fix v-development skill accuracy
Correct v.mod schema (dependencies), manifest optionality, entry-point guidance, VPM registry URL, and globals rule per official V docs.
* Correct mutability and Option/Result propagation guidance
Variables use mut, only struct sections use mut:; postfix ? propagates Options, ! propagates errors; no forced unwrap.
* Scope compilation, nil, and mutability guidance to verified behavior
v run excludes test files; nil only in unsafe/C interop; mutable parameters documented.
* Keep example Config fields immutable
The port field was never mutated; placing it under mut: contradicted the immutable-by-default guidance.
* Recommend json2 over superseded json module
Official V docs teach json2 for encoding/decoding.
