Step 2: real Playwright integration for fetch-page-title

[rockfordlhotka]

Summary

Replaces the HttpClient + regex implementation of fetch-page-title with a real Chromium navigation through Foragent.Browser. Milestone 2 from the project spec (§9.1).

• Foragent.Browser becomes a real library: IBrowserSession + IBrowserSessionFactory (public contracts) backed by PlaywrightBrowserHost (IHostedService owning one shared Chromium per process) and PlaywrightBrowserSessionFactory (fresh IBrowserContext per session, spec §3.5). AddForagentBrowser() extension wires the lot.
• ForagentTaskHandler no longer takes HttpClient; it pulls an IBrowserSession from the factory and disposes it after use. Public A2A contract unchanged.
• Unit tests in Foragent.Agent.Tests use a StubBrowserSessionFactory — no Chromium. Integration tests in Foragent.Browser.Tests exercise the real factory against an in-process Kestrel host serving canned pages (plain title, missing title, HTML entities, JS-rendered title, redirects, 404, session isolation). Chromium is installed on demand into ~/.cache/ms-playwright.
• InternalsVisibleTo("Foragent.Browser.Tests") on Foragent.Browser so integration tests drive the real factory/session without promoting implementation types to public.
• Dockerfile uses mcr.microsoft.com/dotnet/aspnet:10.0 (the Playwright v1.50.0-noble image ships only .NET 8) and installs Chromium + OS deps at image-build time via dotnet exec --runtimeconfig Foragent.Agent.runtimeconfig.json Microsoft.Playwright.dll install chromium --with-deps. Dropped the /app named volume that was masking the fresh image contents.
• docs/framework-feedback.md appended with step-2 observations.

Test plan

• dotnet build --configuration Release — clean, 0 warnings
• dotnet test — 15/15 pass (7 unit tests + 7 Playwright integration tests + 1 placeholder)
• docker compose build foragent succeeds
• Foragent container starts, logs Launching Playwright Chromium + Chromium launched (version 133.x)
• POST http://localhost:5210/ with fetch-page-title against https://example.com returns Example Domain end-to-end (HTTP → auth → bus → handler → Playwright navigation → reply back through bus → HTTP response)

Known limitations (carried to later milestones)

• Still requires the incoming message text to be a bare URL (spec §5.3 LLM-assisted intent translation is future work).
• EchoChatClient still present — Foragent v2 still doesn't do LLM reasoning.
• Playwright NuGet version and Dockerfile base-image tag must stay in sync manually. Flagged as framework feedback.

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