Add the entry tools #2523

Part of #2416 (F-CNT). The last slice: the entry tools agents call over MCP (MCP-01, P1), following the write-tool conventions of #2514. It covers the CNT row of the MCP-01 coverage test (#2517).

Scope

• Core (FluentCMS.Core.Builtin.Tools): EntryTools, a tool provider with
  • list_entries: the entries of a content type with their versions and state.
  • get_entry: an entry with its state, its pointers and the fields of its latest draft or of a named version.
  • get_entry_history: every version of an entry, oldest first.
  • get_resolved_entry: a version read with each entity-field reference replaced by the entity's current published value, and the references that could not be resolved.
  • get_where_used: the entries whose latest draft or published version uses an entry, one field of an entity, or a media asset.
  • create_entry, update_entry and delete_entry: propose a change. The version (none for a delete) and its operation in a change set commit together, into a set named by change_set_id or a session's set, as create_content_type does. An update is based on the entry's published version, so it proposes a create while the entry has never been published. A delete proposes unpublishing the entry. The operation is an entity operation for an entity type.
• Error hints that point an agent at the next call, such as get_schema_document for invalid fields and get_entry after a version conflict.
• Scope (MCP-05): resolved views and where used refuse an entry of a type outside the agent's scope, and where used leaves out the entries an agent may not read.
• The CNT row of McpCoverageTests lists the new tools.

Out of scope

• Entity-specific tools for facts, validity and blast radius (F-ENT F-ENT: Entity registry with sources, validity and blast radius #2417), and media (F-MED F-MED: Media library with required alt text #2427).
• Soft delete and restore as tools: they bypass change sets, so they stay with people for now.
• Amending an operation already in a set, so a second update of one entry in one set is refused as a duplicate, as for content types.
• Moving the change set target into IEntryDirectory, which follows the pattern SCH-05 lands with.

Acceptance

• Over MCP, an agent creates a product entity and a product page that references its price in one set and submits it. A person publishes it, and the agent reads the page resolved with the price, and where used on product.price with the page.
• update_entry from a stale version is refused with a hint to read the entry again; invalid fields come back together, by field, with a hint to read the schema document; a refused write stores no version.
• delete_entry proposes unpublishing; an entry that is not published is refused.
• An agent cannot read, resolve or find usages of entries of types outside its scope.
• Every tool passes ToolProviderConformanceTests and the MCP-01 coverage test.
• Everything above passes on SQLite and PostgreSQL, with no new package.