wasm-tryout: replace todo app with FlagdSchemaAbstraction port (multi-file, DB-backed, WASM + REST)

[Copilot]

Removes the todo-app scaffold from wasm-tryout/Backend and replaces it with a C# port of the TypeScript FlagdSchemaAbstraction class, backed by SQLite/EF Core, with multi-file support, a [JSInvokable] service surface, and a REST-style controller layer.

Deleted

• TodoItem.cs, TodoDbContext.cs, TodoJsonContext.cs, TodoService.cs

New EF Core schema

Three tables in a shared in-memory SQLite database (IndexedDB-persisted via raw byte export/import, same pattern as before):

• flag_files — named schema documents
• flag_entries — flags per file (type, state, valueJson, metadataJson, targetingJson); unique on (file_id, flag_key)
• environment_entries — environment name + JSON-encoded aliases; unique on (file_id, name)

FlagdService ([JSInvokable])

Ports FlagdSchemaAbstraction.fromSchema() / exportSchema() and exposes full CRUD over the WASM boundary:

// Direct JS/WASM calls
Backend.FlagdService.createFile("production.json");
Backend.FlagdService.upsertFlag(fileId, JSON.stringify({ key: "dark-mode", type: "boolean", state: "ENABLED", valueJson: "true" }));
Backend.FlagdService.importSchema(fileId, rawFlagdSchemaJson);
const schema = Backend.FlagdService.exportSchema(fileId); // round-trips to flagd-compatible JSON

ImportSchema parses $evaluators for environment aliases (pattern isXxx) and reconstructs them on export — matching the TypeScript logic exactly.

FlagdController (REST routing layer)

Single [JSInvokable] entry point that dispatches by (method, path):

// Also exposed as window.api() for browser-console testing
window.api("GET",    "/api/files");
window.api("POST",   "/api/files/1/flags",        { key: "my-flag", type: "string", state: "ENABLED" });
window.api("POST",   "/api/files/1/schema",        rawFlagdSchemaJson);
window.api("GET",    "/api/files/1/schema");
window.api("DELETE", "/api/files/1/environments/production");

index.html

Replaced todo UI with a two-panel flagd schema manager: file list, flags table (create/edit/delete), environments table, schema import/export textarea, and IndexedDB persistence.

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