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/cognitive.rs

@@ -61,10 +61,16 @@ pub struct CognitiveEngine {
     pub temporal_searcher: TemporalSearcher,
 }
 
+impl Default for CognitiveEngine {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl CognitiveEngine {
     /// Initialize all cognitive modules with default configurations.
     pub fn new() -> Self {
-        let engine = Self {
+        Self {
             // Neuroscience
             activation_network: ActivationNetwork::new(),
             synaptic_tagging: SynapticTaggingSystem::new(),
@@ -98,8 +104,6 @@ impl CognitiveEngine {
             // Search
             reranker: Reranker::new(RerankerConfig::default()),
             temporal_searcher: TemporalSearcher::new(),
-        };
-
-        engine
+        }
     }
 }