Add meme share button variants

[ohld]

Summary

• Adds a localized share button above private-feed like/skip buttons.
• Supports two Telegram-native share adapters: t.me/share/url deep-link sharing and switch_inline_query_chosen_chat with #meme_id exact inline results.
• Makes /start s_{sharer_user_id}_{meme_id} send the clicked meme first, add the meme language to the user, and defer new-user onboarding until after the first reaction.
• Keeps share parsing and button construction behind src/tgbot/sharing.py so Share Attribution logic has one interface.

Telegram API notes

• t.me/share/url officially supports url + optional text: https://core.telegram.org/api/links#share-links
• switch_inline_query_chosen_chat can prefill query text after chat selection: https://core.telegram.org/bots/api#switchinlinequerychosenchat
• Deep-link start payload is capped at 64 chars and limited to A-Z/a-z/0-9/_/-: https://core.telegram.org/bots/features#deep-linking

Verification

• ruff check src/tgbot/sharing.py src/tgbot/senders/keyboards.py src/tgbot/senders/meme.py src/tgbot/senders/next_message.py src/tgbot/handlers/start.py src/tgbot/handlers/reaction.py src/tgbot/handlers/inline.py src/tgbot/handlers/deep_link.py src/tgbot/service.py src/storage/schemas.py tests/tgbot/test_sharing.py tests/tgbot/test_inline_search.py tests/tgbot/test_meme_like_count_experiment.py tests/tgbot/test_reaction_handler.py tests/tgbot/test_start.py
• pytest -q tests/tgbot/test_sharing.py tests/tgbot/test_inline_search.py tests/tgbot/test_meme_like_count_experiment.py

Not run

• DB-backed tests tests/tgbot/test_reaction_handler.py and tests/tgbot/test_start.py need the docker-compose Postgres hostname app_db; local host run failed with socket.gaierror for app_db.

[ohld]

STAFF ENGINEER REVIEW: CHANGES REQUESTED — inline search share attribution is unsafe with global Telegram caching, and CI lint is red.

Findings:

• src/tgbot/handlers/inline.py:160 returns inline search results whose captions now include s_{user_id}_{meme_id} share links, but the non-exact search answer is still globally cacheable for 12 hours. Telegram can reuse the first user's cached result for another user with the same query, misattributing share rewards. Set is_personal=True for these personalized answers or remove user-specific attribution from globally cached inline results.
• CI lint is red: ruff check src/ tests/ reports unsorted imports in src/tgbot/senders/utils.py:1.

I disabled auto-merge before posting this. No secrets or raw SQL interpolation were found in the new SQL helper, but the cache attribution bug is a reward/accounting integrity issue and blocks approval.

[ohld]

STAFF ENGINEER REVIEW: CHANGES REQUESTED — Existing users can be stranded by shared memes they have already reacted to.

src/tgbot/handlers/start.py:112 fetches and sends the shared meme without checking whether this user already has a user_meme_reaction row for it. send_meme_to_user then calls create_user_meme_reaction, but that insert is ON CONFLICT DO NOTHING on (user_id, meme_id). If the user has already liked/skipped that meme, the button callback later hits update_user_meme_reaction, which only updates rows with reaction_id IS NULL; it returns false and handle_reaction does not call next_message. The user taps like/skip and stays stuck on the shared meme.

Please filter already-reacted shared memes for existing users before sending them, or make the duplicate-reaction path advance to the next meme intentionally. Add a regression test for existing user + share link + already reacted meme.

[ohld]

STAFF ENGINEER REVIEW: APPROVED — current head b828519 is clean. Structural review, CSO diff pass, and Codex review found no blocking issues. Prior blockers are addressed: inline share results are personal-cache safe, already-reacted shared memes are skipped with regression coverage, CI is green. Local verification: ruff check on changed Python files; pytest -q tests/tgbot/test_sharing.py tests/tgbot/test_inline_search.py tests/tgbot/test_meme_like_count_experiment.py.

[ohld]

✅ Approved + merged.