v0.3.0

Unify cross-language release + improve install/access (#21)

Fixes a release trap and makes getting started one page for every language.

Release (the bug): RELEASING.md claimed a single `vX.Y.Z` tag ships all five SDKs,
but the PyPI/npm publish workflows only triggered on `lians-v*` / `lians-ts-v*`, so
`v0.3.0` would have shipped Java/C/Go and SILENTLY skipped Python and npm.
- publish-lian.yml + publish-lian-npm.yml now also trigger on `v*` (old tags kept
  for back-compat). One tag now genuinely releases all five.
- PyPI publish gains skip-existing so re-running a release tag is a no-op.

Version consistency (lock-step 0.3.0):
- C: CMakeLists project(... VERSION 0.3.0 ...).
- Go: new version.go exposing `Version` const at runtime.
- README SDK table: Java 0.2.0 → 0.3.0; "All four" → "All five".
- RELEASING.md version-locations updated for C CMake + Go version.go.

Ease of access:
- New docs/install.md — one-page install matrix + 30-second hello for the server
  and all five languages, linked from the README header and SDK section.
- New TypeScript SDK README (was the only SDK without one).

Co-authored-by: etanbuns <ethan.beirne@aol.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>