Add transform system for modifying components in provider chains (#2836)

* Consolidate tool transformation logic into TransformingProvider

Tool transformations were previously scattered across LocalProvider,
ProxyProvider, and MCPConfig. This consolidates all transformation
logic into TransformingProvider via with_transforms(tool_transforms={...}).

- Add tool_transforms parameter to TransformingProvider
- Add tool_transforms to Provider.with_transforms()
- Remove transformation storage from LocalProvider and ProxyProvider
- Remove add_tool_transformation() and remove_tool_transformation() from FastMCP
- Add tool_transforms parameter to factory methods (from_openapi, from_fastapi, create_proxy)
- Update tests to use new patterns

* Fix: reject tool lookups by pre-transform name

* Add collision validation for tool_transforms and fix docstring examples

- Validate duplicate target names in tool_transforms raise ValueError
- Fix docstring examples to use arguments/ArgTransformConfig (not args/ArgTransform)
- Add test for collision validation

* Add server-level tool transform APIs and fix task registration

- Add AggregateProvider to present multiple providers as one
- Add _get_root_provider() to apply server-level transforms uniformly
- Fix _docket_lifespan to use root provider (ensures renamed tools
  register with correct keys for background execution)
- Add tool_transforms kwarg to __init__ (non-deprecated)
- Add add_tool_transform(), remove_tool_transform(), tool_transforms property
- Deprecate old API names (tool_transformations, add_tool_transformation, etc.)
- Update tests to use new API

* Add graceful degradation for provider errors in AggregateProvider

* Match original behavior: parallel queries with DEBUG logging

* Refactor transforms to middleware-style call_next pattern

Replaces the ad-hoc transformation system with a unified Transform
abstraction using the same call_next pattern as server middleware.

Key changes:
- New src/fastmcp/server/transforms/ module with Transform base class
- Namespace, ToolTransform, Visibility all implement the same interface
- Transforms compose via functools.partial chain building
- Visibility is now just the first transform in provider._transforms
- Server-level transforms apply after provider aggregation
- Task registration now applies full transform chain

Removes TransformingProvider, _BoundTransform, ComponentSource protocol.
User-facing API unchanged: mount(), add_transform(), enable/disable all
work as before.

* Add comprehensive transforms and visibility documentation

New docs/servers/providers/transforms.mdx covering:
- Mental model for middleware-style transform pattern
- Built-in transforms (Namespace, ToolTransform)
- Server vs provider-level transforms and ordering
- Tool modification (immediate vs deferred)
- Custom transform creation

New docs/servers/visibility.mdx covering:
- Enable/disable API for runtime visibility control
- Keys and tags for targeting components
- Allowlist mode with only=True
- Server vs provider visibility layering

Updates existing docs to reference new pages and simplifies
redundant content. Visibility is documented as a user feature,
not as an implementation detail.

* Restructure transforms docs and delete tool-transformation pattern

* Cleanup: simplify get_tasks and remove unused Provider.get_component

* Update loq

* Update loq limits and add loq note to AGENTS.md

* Deprecate add_tool_transformation and tool_transformations param

* Address PR review feedback: remove redundant imports, fix path reference

* Add missing imports to code examples in v3-features.mdx

docs/docs.json

@@ -20,10 +20,7 @@
     "primary": "#2d00f7"
   },
   "contextual": {
-    "options": [
-      "copy",
-      "view"
-    ]
+    "options": ["copy", "view"]
   },
   "description": "The fast, Pythonic way to build MCP servers and clients.",
   "errors": {
@@ -108,10 +105,10 @@
                 "icon": "layer-group",
                 "pages": [
                   "servers/providers/overview",
+                  "servers/providers/transforms",
                   "servers/providers/local",
                   "servers/providers/filesystem",
                   "servers/providers/mounting",
-                  "servers/providers/namespacing",
                   "servers/providers/proxy",
                   "servers/providers/custom"
                 ]
@@ -130,7 +127,8 @@
                   "servers/progress",
                   "servers/sampling",
                   "servers/storage-backends",
-                  "servers/tasks"
+                  "servers/tasks",
+                  "servers/visibility"
                 ]
               },
               {
@@ -163,10 +161,7 @@
               {
                 "group": "Essentials",
                 "icon": "cube",
-                "pages": [
-                  "clients/client",
-                  "clients/transports"
-                ]
+                "pages": ["clients/client", "clients/transports"]
               },
               {
                 "group": "Core Operations",
@@ -193,10 +188,7 @@
               {
                 "group": "Authentication",
                 "icon": "user-shield",
-                "pages": [
-                  "clients/auth/oauth",
-                  "clients/auth/bearer"
-                ]
+                "pages": ["clients/auth/oauth", "clients/auth/bearer"]
               }
             ]
           },
@@ -206,10 +198,7 @@
               {
                 "group": "Providers",
                 "icon": "globe",
-                "pages": [
-                  "integrations/fastapi",
-                  "integrations/openapi"
-                ]
+                "pages": ["integrations/fastapi", "integrations/openapi"]
               },
               {
                 "group": "Authentication",
@@ -263,7 +252,7 @@
           {
             "group": "Patterns",
             "pages": [
-              "patterns/tool-transformation",
+              "patterns/decorating-methods",
               "patterns/cli",
               "patterns/contrib",
               "patterns/testing"
@@ -571,6 +560,14 @@
     {
       "destination": "/servers/providers/mounting",
       "source": "/servers/composition"
+    },
+    {
+      "destination": "/servers/providers/transforms",
+      "source": "/servers/providers/namespacing"
+    },
+    {
+      "destination": "/servers/providers/transforms",
+      "source": "/patterns/tool-transformation"
     }
   ],
   "search": {