feat: modernize embedded PGlite API and OSS tooling

[f0rr0]

Summary

• Modernize the crate around the intended high-level API: Pglite for direct embedded use and PgliteServer for PostgreSQL client compatibility.
• Add process-local template-cluster caching for fast temporary databases, plus fresh_temporary escape hatches.
• Add blocking proxy/server fixes for extended protocol clients, readiness, and socket mode handling.
• Add OSS hygiene: CI, issue/PR templates, rustfmt/clippy/deny configs, asset provenance docs, Tauri guidance, contribution docs, and Conventional Commit validation.
• Add release-plz for manual releases from main: create/update a release PR, dry-run publish, then publish via crates.io Trusted Publishing.
• Add mandatory release intent for package-affecting changes: PRs touching Cargo.toml, Cargo.lock, src/**, assets/**, examples/**, or benches/** must use release-plz-compatible title types (feat, fix, perf, refactor, revert, or breaking !). Docs/CI/repo-only PRs can remain non-release.
• Add a curated CHANGELOG.md, release documentation, package publish restrictions, and crates.io package excludes for repo-only automation/review files.
• Add compatibility coverage for SQLx and tokio-postgres, plus runtime/proxy smoke tests.

Verification

• cargo fmt --all --check
• cargo check --all-targets --locked
• cargo check --no-default-features --all-targets --locked
• /Users/sid/.cargo/bin/cargo-deny check --hide-inclusion-graph
• cargo test --lib --bins --locked
• cargo test --doc --locked
• cargo package --locked --allow-dirty
• cargo publish --locked --dry-run --allow-dirty
• actionlint
• shellcheck .github/scripts/check-conventional-commit.sh .github/scripts/check-release-intent.sh
• taplo check release-plz.toml Cargo.toml
• taplo fmt --check release-plz.toml Cargo.toml
• ruby -e 'require "yaml"; ARGV.each { |f| YAML.load_file(f); puts "ok #{f}" }' .github/workflows/ci.yml .github/workflows/conventional-commits.yml .github/workflows/release.yml
• ./.github/scripts/check-conventional-commit.sh 'chore(release): 0.2.0'
• Release-intent script smoke tests: release title passes, docs title fails for package-affecting changes, release-plz branch/title exemption passes.
• Previous full runtime suite on this branch: cargo test --test runtime_smoke --locked -- --nocapture, cargo test --test proxy_smoke --locked -- --nocapture, and cargo test --test client_compat --locked -- --nocapture.