## Why
The plugin manifest currently has no field for who built a plugin or when. `fulltime-core`'s
Plugins management screen (`openspec/changes/plugin-host-runtime` in `Apps/rust`) lists each
plugin's `id` and `version` only, because that's all the manifest carries — there's nowhere to
show a developer/publisher name or a build timestamp to help a user tell plugins apart or judge
how current one is.
## What Changes
- Add two optional manifest fields: `developer` (a display name/identifier for the plugin's
author or publisher) and `build_date` (an RFC 3339 timestamp for when the plugin was built).
Optional, not required, so existing manifests (e.g. `Plugins/Bundesliga`'s) keep parsing
without changes — an additive, minor-version manifest schema change under this crate's own
versioning policy (see `RELEASING.md`/`src/version.rs`'s doc comments).
- `Manifest::parse` accepts and exposes both fields when present, and treats their absence as
`None` rather than a parse error. Neither field affects host/plugin compatibility checks — both
are display-only metadata, unlike `schema_version`/`interface_version`.
- `build_date` is documented as RFC 3339 (matching the existing `Fixture.kickoff` convention in
`wit/data-provider.wit`) but is not parsed/validated by this crate — same treatment as
`kickoff`, which this crate also never validates. A non-empty check only, matching
`network_hosts` entries.
## Capabilities
### New Capabilities
(none)
### Modified Capabilities
- `plugin-manifest-format`: the manifest schema gains two optional fields, `developer` and
`build_date`, each exposed on the parsed `Manifest` and validated at parse time when present.
## Impact
- **`src/manifest.rs`**: `Manifest` struct gains `developer: Option<String>` and
`build_date: Option<String>` (or a parsed timestamp type — see `design.md`), `RawManifest`
gains the corresponding optional fields, and `Manifest::parse` validates `build_date`'s format
when present.
- **Downstream plugins** (`Plugins/Bundesliga`, future plugins): unaffected unless they choose to
add the new fields to their own `manifest.toml`.
- **`Apps/rust`'s plugin management UI** (`openspec/changes/plugin-host-runtime`, a separate,
already-implemented change in that repo): a follow-up change there would surface these fields
in the Plugins screen once this manifest change ships — out of scope here.