feat: studio.theme.solarized v0.1.0 builds against SDK

Promotes the skeleton to a real WASM plugin component. The
22 KiB stripped artefact at
target/wasm32-wasip2/release/studio_theme_solarized.wasm
is the proof-of-contract for fai-studio-plugin-sdk v0.1.

Implements:

- theme::Guest::theme_for(brightness) returning the
  pinned Solarized Light/Dark palettes (14 ARGB tokens
  each). Brightness names other than "light"/"dark"
  return PluginError::Declined.
- translate::Guest + output_view::Guest as Declined-only
  stubs — v0.1 of the SDK requires all three hooks per
  plugin; v0.2 will split the WIT.

Cargo.toml pins edition 2021 (matches SDK; wit-bindgen
0.36 codegen does not yet support edition 2024).

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

Cargo.toml

@@ -1,28 +1,16 @@
-# SKELETON — does not yet compile.
+# Standalone Cargo.toml — targets wasm32-wasip2.
 #
-# This crate targets the studio-plugin world declared in
-# `wit/studio-plugin.wit`. It cannot be built until two
-# upstream pieces ship:
+# Build:
+#   cargo build --release --target wasm32-wasip2
 #
-#   1. The `fai-studio-plugin-sdk` crate that wraps the WIT
-#      bindings with an ergonomic Rust API (the `#[plugin(theme)]`
-#      attribute referenced in `src/lib.rs`).
-#   2. Studio's plugin-host module that discovers, loads, and
-#      invokes plugin components at GUI startup.
-#
-# Both are documented in `docs/advanced/studio-plugin-sdk.md`.
-# Until they exist, this directory serves three purposes:
-#
-#   - Validates the WIT-file structure by being a real crate that
-#     references it (parse-only path).
-#   - Locks in the exact Solarized colour palette so the
-#     in-tree first plugin doesn't bike-shed at integration time.
-#   - Gives the SDK author a concrete consumer to test against.
+# Output: target/wasm32-wasip2/release/studio_theme_solarized.wasm
 
 [package]
 name = "studio_theme_solarized"
 version = "0.1.0"
-edition = "2024"
+# Track the SDK's edition — wit-bindgen 0.36 codegen does not
+# yet support edition 2024.
+edition = "2021"
 authors = ["Dr. Stefan Flemming <platform@flemming.ai>"]
 license = "Apache-2.0"
 publish = false
@@ -34,9 +22,10 @@ rust-version = "1.85"
 crate-type = ["cdylib"]
 
 [dependencies]
-# Forward-reference: this crate doesn't yet exist. Tracked in
-# docs/advanced/studio-plugin-sdk.md.
-# fai-studio-plugin-sdk = { git = "https://git.flemming.ai/fai/studio-plugin-sdk", branch = "main" }
+# The SDK lives in fai/fai_studio_plugin_sdk during bootstrap;
+# in production this will be a git dependency pointing at
+# https://git.flemming.ai/fai/studio-plugin-sdk.
+fai-studio-plugin-sdk = { path = "../../fai_studio_plugin_sdk" }
 
 [package.metadata.component]
 package = "fai:studio-plugin"