Feature/csharp model name fixer

[haiyuazhang]

Adds a TypeSpec linter rule in @typespec/http-client-csharp that flags single-word model names (e.g. model Document) which collide with BCL or third-party types. The fix flow runs in the typespec-vscode extension:

• Linter: detects single-word model names; also flags @@clientName overrides whose target string is a single word.
• VS Code extension: adds a code action provider that offers two AI fixes via the lightbulb (Ctrl+.):
  1. Rename model directly (uses the language server rename provider so all references are updated).
  2. Override via @@clientName in client.tsp (creates client.tsp if missing, groups inserts after existing @@clientName lines, and auto-adds imports: - ./client.tsp to tspconfig.yaml so the compiler picks it up as a first-class source).
• AI suggestions are fetched on demand via vscode.lm (no external SDK).
• File watcher cleans up the tspconfig.yaml import and nudges open editors to recompile when client.tsp is deleted.
• Adds a manual test workspace under packages/http-client-csharp/linter-test.

How the Codefix Works

Phase 1: Detection (Compilation)

1. Linter rule single-word-model-name.rule.ts runs during compilation
2. Detects models like model Document { ... } — single PascalCase word
3. Reports warning with no codefixes attached (the fixer lives in the VS Code extension, not the linter)
4. 🟡 Yellow squiggly appears under the model name

Phase 2: Menu (Ctrl+.)

5. User presses Ctrl+. on the yellow squiggly
6. VS Code asks the extension's CodeActionProvider (code-action-provider.ts) — not the language server
7. Provider returns two static menu items — no AI call yet, so the menu appears instantly:
   • 💡 Rename model (AI-suggested)
   • 💡 Override via @@clientName (AI-suggested)

Phase 3: AI Suggestion (after user clicks)

8. User clicks one of the menu items → runs SuggestModelName command
9. Command calls vscode.lm directly (no LSP bridge — already in the extension host)
10. Tries model families: gpt-4o, gpt-4, gpt-3.5-turbo, copilot-gpt-4.1
11. AI returns 5 name suggestions
12. Shows a QuickPick dialog with the suggestions:
    • TableDocument (recommended)
    • StorageDocument
    • TableStorageDocument
    • DocumentEntity
    • TableDocumentEntity
13. User picks one

Phase 4: Apply

If "Rename model" was chosen:

14a. Calls vscode.executeDocumentRenameProvider → renames the model across all files, updating all references

If "Override via @@clientName" was chosen:

14b. Creates/edits client.tsp via vscode.WorkspaceEdit:

• Adds import and using lines if missing
• Appends @@clientName(Document, "TableDocument");

15. Calls ensureClientTspImport() → adds imports: - ./client.tsp to tspconfig.yaml
16. Opens client.tsp in the editor
17. Recompilation triggers → getLibraryName() now returns the multi-word name → ✅ warning disappears

[github-actions]

❌ There is undocummented changes. Run chronus add to add a changeset or click here.

The following packages have changes but are not documented.

• ❌typespec-vscode

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