Add custom types, version command, and restore --verify flag

- Add internal/types package with type-safe wrappers for IDs, hashes,
  paths, and credentials (FileID, BlobID, ChunkHash, etc.)
- Implement driver.Valuer and sql.Scanner for UUID-based types
- Add `vaultik version` command showing version, commit, go version
- Add `--verify` flag to restore command that checksums all restored
  files against expected chunk hashes with progress bar
- Remove fetch.go (dead code, functionality in restore)
- Clean up TODO.md, remove completed items
- Update all database and snapshot code to use new custom types

test/config.yaml

@@ -1,9 +1,11 @@
 age_recipients:
   - age1278m9q7dp3chsh2dcy82qk27v047zywyvtxwnj4cvt0z65jw6a7q5dqhfj  # sneak's long term age key
   - age1otherpubkey...  # add additional recipients as needed
-source_dirs:
-  - /tmp/vaultik-test-source
-  - /var/test/data
+snapshots:
+  test:
+    paths:
+      - /tmp/vaultik-test-source
+      - /var/test/data
 exclude:
   - '*.log'
   - '*.tmp'
@@ -25,4 +27,4 @@ index_path: /tmp/vaultik-test.sqlite
 chunk_size: 10MB
 blob_size_limit: 10GB
 compression_level: 3
-hostname: test-host
+hostname: test-host