feat(phase9): migration v14 + storage and Tauri command extension for llm_tags

Adds llm_tags TEXT NOT NULL DEFAULT '' to the transcripts table via
new migration v14. SELECT statements + TranscriptRow + transcript_row_from
now carry the column. update_transcript_meta gains a sixth Option for
llm_tags following the existing COALESCE pattern; an
#[allow(too_many_arguments)] keeps clippy happy without inverting the
signature into a struct that would just shift the indirection.

The Tauri-side TranscriptDto + UpdateTranscriptMetaRequest + the
update_transcript_meta_cmd command pass llm_tags through unchanged.
Pre-existing manualTags persistence path now has a sibling for
llmTags ready for the frontend to call.

Phase 8 brittle test fix included: list_recent_completions_uses_local_day_boundary
was anchoring its "-2 days" UTC offset against the local-day spine,
which drifted across UTC midnight. Anchored to the local date directly
so it matches the spine regardless of clock.

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

src-tauri/src/commands/transcripts.rs

@@ -48,6 +48,8 @@ pub struct TranscriptDto {
     pub template: String,
     pub language: String,
     pub segments_json: String,
+    /// Phase 9 LLM-generated content tags ("topic:...", "intent:...").
+    pub llm_tags: String,
 }
 
 impl From<TranscriptRow> for TranscriptDto {
@@ -68,6 +70,7 @@ impl From<TranscriptRow> for TranscriptDto {
             template: r.template,
             language: r.language,
             segments_json: r.segments_json,
+            llm_tags: r.llm_tags,
         }
     }
 }
@@ -221,6 +224,11 @@ pub struct UpdateTranscriptMetaRequest {
     pub language: Option<String>,
     #[serde(default)]
     pub segments_json: Option<String>,
+    /// Phase 9 LLM content tags. Same comma-joined string convention as
+    /// `manual_tags`. Pass `None` to leave unchanged; pass `Some("")` to
+    /// explicitly clear.
+    #[serde(default)]
+    pub llm_tags: Option<String>,
 }
 
 #[tauri::command]
@@ -237,6 +245,7 @@ pub async fn update_transcript_meta_cmd(
         patch.template.as_deref(),
         patch.language.as_deref(),
         patch.segments_json.as_deref(),
+        patch.llm_tags.as_deref(),
     )
     .await
     .map_err(|e| e.to_string())?;