send_message: verify thread matches target profile, fall back to compose

[huangruoqi]

Summary

• Thread search now prefers a result matching profile hints instead of blindly taking the first visible row
• After opening a thread, verifies the header name and the resolved profile-link URL against the target profile before sending — aborts on mismatch instead of risking a message to the wrong person
• send_message now falls back to the "Compose a new message" typeahead when a connection has no existing thread anywhere (e.g. accepted without a note) — matches the recipient by name and adds them
• New-conversation drafts (.../messaging/thread/new/) have no persisted thread id, so their title bar just reads "New message" — verification now checks the conversation's profile card first, which carries the recipient's name and an already-resolved vanity-slug link (no click-and-navigate needed there)
• Adds testing/tools/send_message.py, a manual live tool for sending a real DM through this flow
• Bumps version to 1.0.0.9 and updates CHANGELOG

Test plan

• testing/tests/test_send_message_thread_match.py covers header-match, profile-URL-match, and compose-fallback cases (including a same-name-wrong-person scenario caught by the resolved URL)
• testing/tools/check_thread_match.py / testing/tools/send_message.py manual check tools

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