Feat v0.2.9 builtin extension retirement

Stop auto-seeding 6 chat-centric extensions on startup. Move them to
standard packages with js/ layout and "requires": ["chat"] metadata.
Delete SeedBuiltinPackages, seed tests, Dockerfile COPY, and
extensions/builtin/ directory.

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

packages/regex-tester/js/script.js

@@ -0,0 +1,102 @@
+// ==========================================
+// Regex Tester — Browser Extension
+// ==========================================
+// Tests regular expressions against input strings.
+// Registers the regex_test tool so the LLM can verify
+// patterns instead of guessing.
+// ==========================================
+
+Extensions.register({
+    id: 'regex-tester',
+
+    async init(ctx) {
+        const self = this;
+
+        ctx.tools.handle('regex_test', async (args) => {
+            return self._test(args.pattern, args.flags || '', args.inputs || []);
+        });
+    },
+
+    _test(pattern, flags, inputs) {
+        // Validate pattern
+        let regex;
+        try {
+            regex = new RegExp(pattern, flags);
+        } catch (e) {
+            return {
+                success: false,
+                error: `Invalid regex: ${e.message}`,
+                pattern,
+                flags,
+            };
+        }
+
+        const results = inputs.map(input => {
+            // Reset lastIndex for global/sticky patterns
+            regex.lastIndex = 0;
+
+            const isGlobal = regex.global;
+            const matches = [];
+
+            if (isGlobal) {
+                // Collect all matches for global flag
+                let match;
+                while ((match = regex.exec(input)) !== null) {
+                    matches.push(this._formatMatch(match));
+                    // Prevent infinite loops on zero-length matches
+                    if (match[0].length === 0) regex.lastIndex++;
+                }
+            } else {
+                const match = regex.exec(input);
+                if (match) {
+                    matches.push(this._formatMatch(match));
+                }
+            }
+
+            return {
+                input,
+                matched: matches.length > 0,
+                matchCount: matches.length,
+                matches,
+            };
+        });
+
+        const totalMatched = results.filter(r => r.matched).length;
+
+        return {
+            success: true,
+            pattern,
+            flags,
+            summary: `${totalMatched}/${inputs.length} inputs matched`,
+            results,
+        };
+    },
+
+    _formatMatch(match) {
+        const result = {
+            fullMatch: match[0],
+            index: match.index,
+            length: match[0].length,
+        };
+
+        // Named groups (ES2018)
+        if (match.groups) {
+            result.namedGroups = {};
+            for (const [name, value] of Object.entries(match.groups)) {
+                result.namedGroups[name] = value;
+            }
+        }
+
+        // Numbered capture groups
+        if (match.length > 1) {
+            result.groups = [];
+            for (let i = 1; i < match.length; i++) {
+                result.groups.push(match[i] !== undefined ? match[i] : null);
+            }
+        }
+
+        return result;
+    },
+
+    destroy() {}
+});