feat(network): Add invitation manager tools

[Aseran20]

Closes #390.

Summary

Adds two new read-only MCP tools that surface the LinkedIn invitation manager:

• get_sent_invitations — outgoing connection requests still awaiting acceptance (/mynetwork/invitation-manager/sent/)
• get_received_invitations — incoming connection requests awaiting your action (/mynetwork/invitation-manager/)

Both return the standard {url, sections, references} shape, with anchor-derived profile URLs in references so callers can chain get_person_profile / connect_with_person naturally.

Implementation Notes

• Both extractor methods mirror the get_inbox pattern: _navigate_to_page → _wait_for_main_text → handle_modal_close → _scroll_main_scrollable_region → _extract_root_content(['main']) → strip_linkedin_noise → build_references. No new helpers, no class-name selectors.
• limit defaults to 50 (versus 20 for get_inbox) since invitation lists tend to be longer-lived; capped at 100 via Field(ge=1, le=100).
• Network-graph operations land in a new tools/network.py module to keep them distinct from messaging. server.py is updated to register them; tests/test_tools.py gets matching mock entries plus a TestNetworkTools class and the new tool names in the global timeout assertion.
• README tool status table updated.

Verification

• uv run ruff check .: clean
• uv run ruff format .: clean
• uv run ty check: clean
• uv run pytest: 385 passed, 5 skipped (Windows POSIX-permission skips), 2 pre-existing Docker-runtime failures unrelated to this change (verified by checking out main and reproducing).
• New unit tests: TestNetworkTools covers success path for both tools plus a custom-limit forwarding test.
• Live end-to-end against mynetwork/invitation-manager/sent/ not run in this PR; happy to follow the AGENTS.md curl-based protocol if a maintainer wants me to capture a sample payload before merge.

Synthetic prompt

Add two new MCP tools, get_sent_invitations and get_received_invitations, exposing the LinkedIn invitation manager pages (sent and received). Place them in a new tools/network.py module to keep them distinct from messaging. Mirror the get_inbox extractor pattern (navigate → scroll → extract → build_references). Wire registration in server.py, extend the test mock and add TestNetworkTools covering success + custom limit, update the README tool status table, and update the global timeout assertion to include the new tool names.

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