chore(llm): update callers for renamed model variants

Picks up the registry rename in the front-end and Tauri command layer:

- src/lib/types/app.ts: LlmModelIdStr now lists the four new ids
  (qwen3_5_2b / qwen3_5_4b / qwen3_5_9b / qwen3_6_27b).
- src/lib/pages/SettingsPage.svelte: LLM_MODELS table rebuilt with
  four tiers (Minimal / Standard / High / Maximum), matching subtitles
  and download-size copy. selectedLlmModelId fallback, hardware-warning
  thresholds, tier-availability check, and ensureRecommendedLlmTier
  fallback all retargeted at the new ids. The Maximum tier surfaces a
  64 GB / 24 GB warning so users with mid-range hardware see honest
  expectations.
- src-tauri/src/commands/llm.rs and commands/tasks.rs: doc-comment
  examples refreshed (Qwen3 4B → Qwen3.5 4B, Qwen3's tokenizer →
  Qwen's tokenizer — the BPE family is shared).
- src/lib/stores/llmStatus.svelte.ts: chip-detail example updated.

cargo build --workspace clean. cargo test --workspace clean.
npx svelte-check reports one pre-existing error in vite.config.js
(unused @ts-expect-error directive, dates back to the original
scaffold commit 9926a42); not introduced here, out of scope to fix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/types/app.ts

@@ -11,7 +11,11 @@ export type WhisperModelSize =
   | "Medium"
   | "Distil-L";
 export type AiTier = "off" | "cleanup" | "tasks";
-export type LlmModelIdStr = "qwen3_1_7b" | "qwen3_4b_instruct_2507" | "qwen3_14b";
+export type LlmModelIdStr =
+  | "qwen3_5_2b"
+  | "qwen3_5_4b"
+  | "qwen3_5_9b"
+  | "qwen3_6_27b";
 export type LlmPromptPreset = "default" | "email" | "notes" | "code";
 export type AiGpuConcurrency = "parallel" | "sequential";
 export type TaskBucket = "inbox" | "today" | "soon" | "later";