chore: license AGPL-3.0, zero clippy warnings, CHANGELOG through v1.6.0

License:
- Replace MIT/Apache-2.0 with AGPL-3.0-only across all crates and npm packages
- Replace LICENSE file with official GNU AGPL-3.0 text
- Remove LICENSE-MIT and LICENSE-APACHE

Code quality:
- Fix all 44 clippy warnings (zero remaining)
- Collapsible if statements, redundant closures, manual Option::map
- Remove duplicate #[allow(dead_code)] attributes in deprecated tool modules
- Add Default impl for CognitiveEngine
- Replace manual sort_by with sort_by_key

Documentation:
- Update CHANGELOG with v1.2.0, v1.3.0, v1.5.0, v1.6.0 entries
- Update README with v1.6.0 highlights and accurate stats (52K lines, 1100+ tests)
- Add fastembed-rs/ to .gitignore
- Add fastembed-rs to workspace exclude

1115 tests passing, zero warnings, RUSTFLAGS="-Dwarnings" clean.

crates/vestige-mcp/src/tools/dedup.rs

@@ -175,7 +175,7 @@ pub async fn execute(
 
         for i in 0..n {
             for j in (i + 1)..n {
-                let sim = cosine_similarity(&filtered_embeddings[i].2, &filtered_embeddings[j].2);
+                let sim = cosine_similarity(filtered_embeddings[i].2, filtered_embeddings[j].2);
                 if sim >= threshold {
                     uf.union(i, j);
                     similarities.push((i, j, sim));
@@ -195,7 +195,7 @@ pub async fn execute(
             .into_values()
             .filter(|c| c.len() > 1)
             .collect();
-        clusters.sort_by(|a, b| b.len().cmp(&a.len()));
+        clusters.sort_by_key(|b| std::cmp::Reverse(b.len()));
         clusters.truncate(limit);
 
         // Build similarity lookup for formatting