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/bin/cli.rs

@@ -561,11 +561,10 @@ fn run_backup(output: PathBuf) -> anyhow::Result<()> {
     }
 
     // Create parent directories if needed
-    if let Some(parent) = output.parent() {
-        if !parent.exists() {
+    if let Some(parent) = output.parent()
+        && !parent.exists() {
             std::fs::create_dir_all(parent)?;
         }
-    }
 
     // Copy the database file
     println!("Copying database...");
@@ -638,11 +637,10 @@ fn run_export(
         .iter()
         .filter(|node| {
             // Date filter
-            if let Some(ref since_dt) = since_date {
-                if node.created_at < *since_dt {
+            if let Some(ref since_dt) = since_date
+                && node.created_at < *since_dt {
                     return false;
                 }
-            }
             // Tag filter: node must contain ALL specified tags
             if !tag_filter.is_empty() {
                 for tag in &tag_filter {
@@ -671,11 +669,10 @@ fn run_export(
     println!();
 
     // Create parent directories if needed
-    if let Some(parent) = output.parent() {
-        if !parent.exists() {
+    if let Some(parent) = output.parent()
+        && !parent.exists() {
             std::fs::create_dir_all(parent)?;
         }
-    }
 
     let file = std::fs::File::create(&output)?;
     let mut writer = BufWriter::new(file);