Migrate conversation search to use PERSONAL_SUPERPOWERS_DIR

Updates conversation indexing and search to use the new personal superpowers
directory structure with environment variable support.

Changes:
- Added src/paths.ts for centralized directory resolution
- Updated db.ts, indexer.ts, verify.ts to use paths.ts
- Created migrate-to-config.sh for data migration from ~/.clank
- Updated all documentation references from ~/.clank to ~/.config/superpowers
- Database paths automatically updated during migration

Migration tested with 5,017 conversations and 6,385 exchanges.

skills/collaboration/remembering-conversations/tool/src/paths.ts

@@ -0,0 +1,56 @@
+import os from 'os';
+import path from 'path';
+
+/**
+ * Get the personal superpowers directory
+ *
+ * Precedence:
+ * 1. PERSONAL_SUPERPOWERS_DIR env var (if set)
+ * 2. XDG_CONFIG_HOME/superpowers (if XDG_CONFIG_HOME is set)
+ * 3. ~/.config/superpowers (default)
+ */
+export function getSuperpowersDir(): string {
+  if (process.env.PERSONAL_SUPERPOWERS_DIR) {
+    return process.env.PERSONAL_SUPERPOWERS_DIR;
+  }
+
+  const xdgConfigHome = process.env.XDG_CONFIG_HOME;
+  if (xdgConfigHome) {
+    return path.join(xdgConfigHome, 'superpowers');
+  }
+
+  return path.join(os.homedir(), '.config', 'superpowers');
+}
+
+/**
+ * Get conversation archive directory
+ */
+export function getArchiveDir(): string {
+  // Allow test override
+  if (process.env.TEST_ARCHIVE_DIR) {
+    return process.env.TEST_ARCHIVE_DIR;
+  }
+
+  return path.join(getSuperpowersDir(), 'conversation-archive');
+}
+
+/**
+ * Get conversation index directory
+ */
+export function getIndexDir(): string {
+  return path.join(getSuperpowersDir(), 'conversation-index');
+}
+
+/**
+ * Get database path
+ */
+export function getDbPath(): string {
+  return path.join(getIndexDir(), 'db.sqlite');
+}
+
+/**
+ * Get exclude config path
+ */
+export function getExcludeConfigPath(): string {
+  return path.join(getIndexDir(), 'exclude.txt');
+}