feat(related): add semantic similarity discovery command

Implement `lore related` command for discovering semantically similar entities
using vector embeddings. Supports two modes:

Entity mode:
  lore related issues 42     # Find entities similar to issue #42
  lore related mrs 99        # Find entities similar to MR !99

Query mode:
  lore related "auth bug"    # Find entities matching free text query

Key features:
- Uses existing embedding infrastructure (nomic-embed-text via Ollama)
- Computes shared labels between source and results
- Shows similarity scores as percentage (0-100%)
- Warns when all results have low similarity (<30%)
- Warns for short queries (<=2 words) that may produce noisy results
- Filters out discussion/note documents, returning only issues and MRs
- Handles orphaned documents gracefully (skips if entity deleted)
- Robot mode JSON output with {ok, data, meta} envelope

Implementation details:
- distance_to_similarity() converts L2 distance to 0-1 score: 1/(1+distance)
- Uses saturating_add/saturating_mul for overflow safety on limit parameter
- Proper error handling for missing embeddings ("run lore embed first")
- Project scoping via -p flag with fuzzy matching

CLI integration:
- Added to autocorrect.rs command registry
- Added Related variant to Commands enum in cli/mod.rs
- Wired into main.rs with handle_related()

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cli/mod.rs

@@ -293,6 +293,28 @@ pub enum Commands {
         project: Option<String>,
     },
 
+    /// Find semantically related entities via vector search
+    #[command(after_help = "\x1b[1mExamples:\x1b[0m
+  lore related issues 42                  # Find entities related to issue #42
+  lore related mrs 99 -p group/repo       # Related to MR #99 in specific project
+  lore related 'authentication flow'      # Find entities matching free text query
+  lore --robot related issues 42 -n 5     # JSON output, limit 5 results")]
+    Related {
+        /// Entity type (issues, mrs) or free text query
+        query_or_type: String,
+
+        /// Entity IID (required when first arg is entity type)
+        iid: Option<i64>,
+
+        /// Maximum results
+        #[arg(short = 'n', long, default_value = "10")]
+        limit: usize,
+
+        /// Scope to project (fuzzy match)
+        #[arg(short, long)]
+        project: Option<String>,
+    },
+
     /// Manage cron-based automatic syncing
     #[command(after_help = "\x1b[1mExamples:\x1b[0m
   lore cron install                       # Install cron job (every 8 minutes)