feat: studio-theme-solarized v0.1.0 — skeleton

First Studio plugin in the new `studio.*` capability namespace.
SKELETON — does not yet compile.

Why ship the skeleton now:

  * Pins Ethan Schoonover's Solarized palette as two const
    Material 3 ColorScheme arrays so the in-tree reference
    doesn't bike-shed at SDK-integration time.
  * Gives the future fai-studio-plugin-sdk author a concrete
    consumer to validate the generated `#[plugin(theme)]`
    macro output against.
  * Validates that the WIT in fai/platform parses by being a
    real crate that references it.

What it does NOT yet do:

  * Compile. The `fai-studio-plugin-sdk` dependency it points
    at doesn't exist. Tracked in
    `fai/platform/docs/advanced/studio-plugin-sdk.md`.
  * Plug into Studio. The plugin-host module that would
    discover and invoke this component lives in the same
    deferred-Phase-1 work.

What it ships:

  * module.yaml declaring `provides: studio.theme.solarized`
    and `studio_extension.hooks: [theme]`.
  * Cargo.toml with the future SDK dependency commented out,
    crate-type=cdylib, component metadata.
  * src/lib.rs with both Solarized colour palettes
    (SOLARIZED_LIGHT and SOLARIZED_DARK), 14 ARGB tokens
    each in Material 3 order, plus the future `#[plugin]`
    function body commented out and two sanity tests on the
    palette constants.
  * README.md explaining the status and the steps to finish
    the plugin once the SDK ships.

Signed-off-by: flemming-it <sf@flemming.it>

README.md

@@ -0,0 +1,42 @@
+# studio-theme-solarized
+
+First in-tree Studio plugin, by way of being the smallest one
+the Studio plugin design supports: a theme.
+
+## Status
+
+**Skeleton.** The crate compiles to the Cargo manifest level but
+not to a `.wasm` artefact, because the dependency it points at
+(`fai-studio-plugin-sdk`) does not exist yet.
+
+Why ship the skeleton now: pins the Solarized colour palette so
+the in-tree reference doesn't bike-shed at integration time, and
+gives the future SDK author a concrete consumer to test the
+generated `#[plugin(theme)]` macro output against.
+
+Tracked in:
+- `docs/advanced/studio-plugin-sdk.md` (SDK design)
+- `docs/advanced/studio-plugins.md` (plugin subsystem overview)
+- `docs/advanced/system-gaps.md#s-21`
+
+## Palette
+
+Ethan Schoonover's [Solarized](https://ethanschoonover.com/solarized/).
+14 Material 3 tokens per brightness, in the order Studio expects
+(primary → on-primary → secondary → … → outline-variant).
+
+The Light and Dark schemes are explicit constants in `src/lib.rs`
+so the file's history is a self-contained record of the palette
+choice. Bike-shed there if at all.
+
+## How to finish this plugin
+
+When the SDK lands:
+
+1. Uncomment the `fai-studio-plugin-sdk` dependency in
+   `Cargo.toml`.
+2. Uncomment the `#[plugin(theme)]` block in `src/lib.rs`.
+3. `cargo build --release --target wasm32-wasip2`.
+4. `fai pack . -o studio-theme-solarized-0.1.0.fai`.
+5. Add to seed.yaml (or to a `studio-plugins/` channel — open
+   decision; see docs/advanced/studio-plugins.md).