Upload local images as blobs and replace paths with CIDs in markdown content.
Remove links to unpublished notes to avoid dangling references.

github.action_repository/ref inside a composite action resolve to the
current step's action (actions/checkout), not the parent composite
action. Use github.action_path which points to the already-downloaded
action source.

The state file is rebuilt from the PDS by `sequoia sync` on every run,
so committing it is unnecessary and caused failures when .gitignore
blocked the `git add`.

The CLI uses crypto.subtle in getContentHash() but relied on the
Bun-global crypto object. This fails in Node.js environments (e.g.
GitHub Actions). Explicitly importing from node:crypto works in both.

Allows users to publish their content to ATProtocol by adding
a single step to their GitHub Actions workflow. Includes state
sync, publish, and optional commit-back of updated frontmatter.

Added a `--verbose` flag to `publish` that shows the post URL. Unfortunately, the resolved source path may not be the rended page path, but at least the CLI will show it now.

Resolves #1

- Adds interactive command to update either the sequoia.json config or
the atproto publication record

Adds a new `stripDatePrefix` configuration option that removes
YYYY-MM-DD- prefixes from filenames when deriving slugs. This
supports Jekyll-style post naming where files like
`2024-01-15-my-post.md` should produce slug `my-post`.