Add restricted-agent examples to common.ai toolset guides

[kaxil]

The toolset guides list their limiting parameters one by one. None showed them set together, or what the model sees when a limit refuses a call, so a reader could not tell how locked down an agent actually is. The SQL, hook, object storage, DataFusion and Agent Skills guides now each have a "Restricting the agent" section with three parts:

• one example Dag that sets every limit the toolset offers, with a comment on each line;
• the exact message the model gets back for each refused call;
• the credential scoping that still holds if a toolset-level check has a gap.

Guide	What the section shows
SQL	allowed_tables, allowed_functions and read-only mode refusing queries; the error each budget raises when exhausted (max_retries, tool_calls_limit); and the database role refusing the same query when allowed_tables is unset
Hook	allowed_methods and pinned_arguments refusing calls; a hook exception failing the task
Object storage	refusals for .., schemes, absolute paths, images and oversized files, none of which use max_retries
DataFusion	an unregistered table, a URL inside the SQL and a CREATE statement all refused
Agent Skills	exclude_tools and exclude_resources hiding tools and files

Gotchas

Two behaviours surfaced while capturing these, and both pages now describe them as they are:

• The pinned-argument message. The hook guide said a model-supplied pinned argument is refused with a message that the argument is fixed. For a method with named parameters, such as S3Hook.read_key, argument validation rejects it first with a generic Extra inputs are not permitted. The toolset's own "is fixed" message only fires when the method also takes **kwargs.
• One correction for skills tools. AgentSkillsToolset has no max_retries, and pydantic-ai-skills sets 1 on its tools, so a second wrong resource name in a row fails the run. Raising the agent's retries does not change that. Exposing the setting is a separate code change.

Every quoted message was captured from a run against Postgres for the SQL example and an S3-compatible endpoint for the others. Each example Dag also ran end to end through AgentOperator with dag.test(), once with a scripted model and once with a real one, and every run finished in success. breeze build-docs common.ai, including the spell check, passes.

A companion PR adds an overview table to the toolsets index and an MCP .filtered() example. The two touch different parts of the same pages and merge cleanly in either order.

[vatsrahul1001]

LGTM, Static checks failure not related to this PR. I have a fix for it #74390