fix(kon): security audit fixes — CSP, XSS, unwraps, key rename

Security fixes from code audit:
- CSP re-enabled in tauri.conf.json with strict directives
  (was null — critical vulnerability)
- XSS fix in viewer highlightText(): HTML entities escaped before
  inserting <mark> tags via {@html}
- Removed 3 unwrap() calls in rule_based.rs British English conversion
  — replaced with safe let-else guards
- Removed unwrap() on main window lookup in lib.rs setup — now uses
  if-let for graceful handling
- Wrapped JSON.parse in DictationPage transcription-result listener
  with try/catch

Rebrand cleanup:
- Renamed all localStorage keys from ramble_* to kon_* across
  7 files (stores, viewer, float, history)

12 tests passing, clippy clean.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/ai-formatting/src/rule_based.rs

@@ -113,7 +113,10 @@ pub fn to_british_english(text: &str) -> String {
         if let Ok(re) = regex_lite::Regex::new(&pattern) {
             result = re
                 .replace_all(&result, |caps: &regex_lite::Captures| {
-                    let matched = caps.get(0).unwrap().as_str();
+                    let Some(m) = caps.get(0) else {
+                        return String::new();
+                    };
+                    let matched = m.as_str();
                     let us_base = us.replace("\\b", "");
                     let base_len = us_base.len();
                     let suffix = if matched.len() > base_len {
@@ -121,12 +124,17 @@ pub fn to_british_english(text: &str) -> String {
                     } else {
                         ""
                     };
-                    let first_char = matched.chars().next().unwrap();
+                    let Some(first_char) = matched.chars().next() else {
+                        return String::new();
+                    };
                     let uk_clean = uk.replace("\\b", "");
                     if first_char.is_uppercase() {
                         let mut chars = uk_clean.chars();
+                        let Some(first_uk) = chars.next() else {
+                            return String::new();
+                        };
                         let upper_first: String =
-                            chars.next().unwrap().to_uppercase().collect();
+                            first_uk.to_uppercase().collect();
                         format!(
                             "{}{}{}",
                             upper_first,