ci: add release pipeline + cut v0.1.1

[ehsanbigzad]

Sets up the dev → main flow with minimal CI and an automated release pipeline.

What this PR adds

File	Role
`.github/workflows/pr-check.yml`	Runs `cargo check --workspace --all-features` on every PR to `main`. Fast (~1 min cached), just verifies it compiles.
`.github/workflows/publish.yml`	On push to `main`, reads the crate version from Cargo.toml. If no tag exists for that version, creates the tag, runs `cargo publish`, and creates the GitHub release with auto-generated notes.
`scripts/release.sh`	Local one-shot: `./scripts/release.sh 0.2.0` bumps version on `dev`, commits, pushes, opens a release PR.

New flow

Everyday work

1. Branch off `dev`, push, open PR `dev` → `main`.
2. `cargo check` runs.
3. Review, merge.

Releases

1. `./scripts/release.sh 0.2.0`.
2. Review + merge the auto-opened release PR.
3. Tag + crates.io publish + GitHub release happen automatically.

Before merging

You'll need to do these one-time setups, otherwise the publish workflow can't function:

1. Add repo secret `CARGO_REGISTRY_TOKEN` at https://github.com/postcrate/core/settings/secrets/actions (scope: publish-update for crate postcrate-core).
2. Set up branch protection on `main` to require PRs + the `cargo check` status check.
3. Install `cargo-edit` locally if you don't have it: `cargo install cargo-edit` (only needed to use `./scripts/release.sh`).