* enables building slurp as a proper nix package
* includes dev shell with rust toolchain and dependencies
* uses rustPlatform.buildRustPackage with cargo lock
* adds flake-utils for cross-platform support

This allows referencing slurp as a flake input in nixos config
without requiring --impure flag or absolute paths.

Hard cutover from Fever API to Miniflux-compatible v1 API with
DB as source of truth for categories/feeds/items.

* add migrations for items.is_starred and items.changed_at
* remove fever handler, routes, and all fever tests
* replace destructive sync_config with one-time legacy bootstrap
that only imports from config when DB is empty
* add miniflux auth middleware (X-Auth-Token + HTTP Basic)
* implement full miniflux endpoint surface: categories/feeds/entries
CRUD, counters, icons, OPML export, bookmarks, health, version
* add broadcast channel for manual feed refresh triggers
* replace CLI auth/add commands with token generator and DB-based
OPML import
* add 30 integration tests covering auth, CRUD, filtering, and
status updates

Co-authored-by: Claude <noreply@anthropic.com>

* implement `before` timestamp parameter for mark feed/group read operations
* add `mark_group_read` db function to mark all items in a group as read
* filter items by COALESCE(published_at, created_at) < before timestamp
* add integration and unit tests for new mark operations

The Fever API spec supports a `before` parameter that allows clients to
mark only items older than a given timestamp as read, which is useful
for partial sync operations.