Migrate capabilities to RockBot.A2A IAgentSkillHandler once MarimerLLC/rockbot#283 ships

[rockfordlhotka]

Context

Foragent introduced ICapability + ForagentTaskHandler (a DI-resolved dispatcher) in step 3 to grow the skill surface without the single-handler-per-agent pattern that the RockBot framework provides today via IAgentTaskHandler.

Upstream tracking: MarimerLLC/rockbot#283 proposes moving that dispatch pattern into the framework as IAgentSkillHandler + AddSkillHandler<T>(), with the framework auto-wiring IAgentTaskHandler and auto-populating AgentCard.Skills.

When rockbot#283 ships (estimated RockBot 0.9.x), Foragent should migrate to it.

What to delete once the framework supports it

• src/Foragent.Capabilities/ICapability.cs
• src/Foragent.Capabilities/ForagentTaskHandler.cs (dispatcher — framework replaces it)
• src/Foragent.Capabilities/ForagentCapabilitiesServiceCollectionExtensions.cs — replaced by individual AddSkillHandler<T>() calls
• ForagentCapabilities.Skills static array — framework will derive the card from registered handlers
• tests/Foragent.Agent.Tests/ForagentTaskHandlerTests.cs — tests the dispatcher we're deleting

What to change

• FetchPageTitleCapability and ExtractStructuredDataCapability implement IAgentSkillHandler instead of ICapability. The existing SkillDefinition / ExecuteAsync signatures are already identical in spirit, so the rename should be mechanical.
• src/Foragent.Agent/Program.cs — replace agent.Services.AddForagentCapabilities() with two agent.AddSkillHandler<T>() calls; remove the manual opts.Card.Skills = [..ForagentCapabilities.Skills] assignment and the matching opts.Skills = [..] override on AddA2AHttpGateway (framework populates both sides of the card from the registered handlers).
• src/Foragent.Agent/appsettings.json — Gateway:Skills can be removed entirely if it hasn't been already (it's already effectively ignored since we override at startup).

Acceptance

• Both capabilities still pass their unit tests (mocking the browser + LLM as they do today) after the migration — the ExecuteAsync method body doesn't need to change.
• The docker-compose smoke path (Blazor → RockBot → Foragent over A2A) still returns the same results for both fetch-page-title and extract-structured-data.
• docs/framework-feedback.md gets a "Step 3 observation resolved" note linking to the delivered rockbot PR.

Do not do before upstream ships

The migration is a no-op until RockBot.A2A exposes IAgentSkillHandler. Pin this to the first RockBot release that includes rockbot#283; don't try to emulate the shape in-repo first.