docs: add limitations and "who it's not for" sections

Be upfront about WASM overhead, WASI constraints, and abstraction layer trade-offs.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

docs: add limitations and "who it's not for" sections

Be upfront about WASM overhead, WASI constraints, and abstraction layer trade-offs.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

feat: add --version flag with release version injection

- Shows "dev (unknown)" for local builds
- Shows "v0.1.4" for release builds via ldflags

Co-Authored-By: Claude Opus 4.5 <[email protected]>

docs: add capability-based security docs link

Co-Authored-By: Claude Opus 4.5 <[email protected]>

docs: add extensibility feature with Registry docs link

Co-Authored-By: Claude Opus 4.5 <[email protected]>

docs: consolidate docs, add pkg.go.dev documentation

- Add doc.go for executor and hostfunc packages
- Add doc comments to all exported types and functions
- Consolidate python.md, javascript.md, host-functions.md into sandbox-api.md
- Remove api.md (covered by pkg.go.dev)
- Update README to link pkg.go.dev for Go API
- Add mock language for executor tests (WASM binary)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

docs: consolidate docs, add pkg.go.dev documentation

- Add doc.go for executor and hostfunc packages
- Add doc comments to all exported types and functions
- Consolidate python.md, javascript.md, host-functions.md into sandbox-api.md
- Remove api.md (covered by pkg.go.dev)
- Update README to link pkg.go.dev for Go API
- Add mock language for executor tests (WASM binary)

Co-Authored-By: Claude Opus 4.5 <[email protected]>