feat(cli+mcp): vertical extractor support (28 extractors discoverable + callable)

Wires the vertical extractor catalog into both the CLI and the MCP
server so users don't have to hit the HTTP API to invoke them. Same
semantics as `/v1/scrape/{vertical}` + `/v1/extractors`.

CLI (webclaw-cli):
- New subcommand `webclaw extractors` lists all 28 extractors with
  name, label, and sample URL. `--json` flag emits the full catalog
  as machine-readable JSON.
- New subcommand `webclaw vertical <name> <url>` runs a specific
  extractor and prints typed JSON. Pretty-printed by default; `--raw`
  for single-line. Exits 1 with a clear "URL does not match" error
  on mismatch.
- FetchClient built with Firefox profile + cloud fallback attached
  when WEBCLAW_API_KEY is set, so antibot-gated verticals escalate.

MCP (webclaw-mcp):
- New tool `list_extractors` (no args) returns the catalog as
  pretty-printed JSON for in-session discovery.
- New tool `vertical_scrape` takes `{name, url}` and returns typed
  JSON. Reuses the long-lived self.fetch_client.
- Tool count goes from 10 to 12. Server-info instruction string
  updated accordingly.

Tests: 215 passing, clippy clean. Manual surface-tested end-to-end:
CLI prints real Reddit/github/pypi data; MCP JSON-RPC session returns
28-entry catalog + typed responses for pypi/requests + rust-lang/rust
in 200-400ms.

Version bumped to 0.5.2 (minor for API additions, backwards compatible).

crates/webclaw-mcp/src/tools.rs

@@ -103,3 +103,20 @@ pub struct SearchParams {
     /// Number of results to return (default: 10)
     pub num_results: Option<u32>,
 }
+
+/// Parameters for `vertical_scrape`: run a site-specific extractor by name.
+#[derive(Debug, Deserialize, JsonSchema)]
+pub struct VerticalParams {
+    /// Name of the vertical extractor. Call `list_extractors` to see all
+    /// available names. Examples: "reddit", "github_repo", "pypi",
+    /// "trustpilot_reviews", "youtube_video", "shopify_product".
+    pub name: String,
+    /// URL to extract. Must match the URL patterns the extractor claims;
+    /// otherwise the tool returns a clear "URL mismatch" error.
+    pub url: String,
+}
+
+/// `list_extractors` takes no arguments but we still need an empty struct
+/// so rmcp can generate a schema and parse the (empty) JSON-RPC params.
+#[derive(Debug, Deserialize, JsonSchema)]
+pub struct ListExtractorsParams {}