fix(web): preserve top-level error envelope on unconfigured systems

Surfaced by local E2E behavior-parity testing of PR vs origin/main: the
plugin-migrated dispatchers were quietly changing the error envelope
shape returned to function-calling models on unconfigured systems.

Two findings, both from per-result error wrapping bleeding into the
pre-flight configuration error path:

1. **search**: ``firecrawl.search()`` caught the
   ``ValueError("Web tools are not configured...")`` from
   ``_get_firecrawl_client()`` and returned it as
   ``{"success": False, "error": ...}``, losing the legacy
   ``{"error": "Error searching web: ..."}`` envelope that
   ``tool_error()`` emits on main. Models that special-case the
   ``error`` key still detect the failure, but the prefix is part of
   the legacy contract some users rely on.

2. **crawl**: ``firecrawl.crawl()`` caught the same pre-flight
   ``ValueError`` and wrapped it as a per-page error inside
   ``results[0]``. Main short-circuits on ``check_firecrawl_api_key()``
   BEFORE dispatching, so its unconfigured response is
   ``{"success": False, "error": "web_crawl requires Firecrawl..."}``
   at the top level. The PR's per-page burying hid the failure inside
   ``results[]`` where models that check ``result.get("error")`` would
   miss it.

Fix:
- ``plugins/web/firecrawl/provider.py``: pull
  ``_get_firecrawl_client()`` outside the broad ``try`` in
  ``search()``. Pre-flight ``ValueError`` / ``ImportError`` propagate
  to the dispatcher's top-level exception handler. In-flight SDK
  errors still get wrapped as ``{"success": False, ...}``.
- ``tools/web_tools.py``: mirror main's upstream availability gate in
  ``web_crawl_tool``. When the resolved crawl provider is
  ``is_available()==False``, short-circuit BEFORE dispatching with the
  same top-level error shape main emits.
- ``tests/tools/test_web_providers.py``: 2 regression tests
  (``TestUnconfiguredErrorEnvelopeParity``) lock in the behavior so
  future plugin work can't undo this.

Verified via local subprocess-based parity test (14/14 scenarios match
origin/main shape exactly) and full 210/210 web test suite green.

plugins/web/firecrawl/provider.py

@@ -390,22 +390,28 @@ class FirecrawlWebSearchProvider(WebSearchProvider):
         Sync; matches the legacy ``_get_firecrawl_client().search(...)``
         call directly. Normalizes the response across SDK/direct/gateway
         shapes via :func:`_extract_web_search_results`.
+
+        Pre-flight errors (``ValueError`` from configuration check,
+        ``ImportError`` from missing SDK) propagate to the dispatcher's
+        top-level handler, which wraps them as ``tool_error(...)`` —
+        matching the legacy ``{"error": "Error searching web: ..."}``
+        envelope. Only in-flight errors are caught and surfaced as
+        ``{"success": False, "error": ...}``.
         """
+        from tools.interrupt import is_interrupted
+
+        if is_interrupted():
+            return {"success": False, "error": "Interrupted"}
+
+        logger.info("Firecrawl search: '%s' (limit=%d)", query, limit)
+        # _get_firecrawl_client() raises ValueError on unconfigured systems —
+        # let it propagate so the dispatcher emits the legacy envelope shape.
+        client = _get_firecrawl_client()
         try:
-            from tools.interrupt import is_interrupted
-
-            if is_interrupted():
-                return {"success": False, "error": "Interrupted"}
-
-            logger.info("Firecrawl search: '%s' (limit=%d)", query, limit)
-            response = _get_firecrawl_client().search(query=query, limit=limit)
+            response = client.search(query=query, limit=limit)
             web_results = _extract_web_search_results(response)
             logger.info("Firecrawl: found %d search results", len(web_results))
             return {"success": True, "data": {"web": web_results}}
-        except ValueError as exc:
-            return {"success": False, "error": str(exc)}
-        except ImportError as exc:
-            return {"success": False, "error": f"Firecrawl SDK not installed: {exc}"}
         except Exception as exc:  # noqa: BLE001
             logger.warning("Firecrawl search error: %s", exc)
             return {"success": False, "error": f"Firecrawl search failed: {exc}"}