docs: justify phone_collector as aiogram-dialog migration exception (#2055)

[yastman]

This pull request was created by @kiro-agent on behalf of @yastman 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
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Summary

Per the issue body, CRM quick actions (#2053) and the demo handler (#2054) are migrating to aiogram-dialog, but phone_collector should stay on raw aiogram Router + FSMContext. Reason:

• Telegram lead capture uses KeyboardButton(request_contact=True) inside ReplyKeyboardMarkup. One tap sends a verified Contact payload.
• aiogram-dialog renders inline-keyboard Select/Button widgets and does not provide a request_contact widget.
• A forced migration would replace one-tap contact share with manual phone typing, measurably reducing opt-in rate for lead capture.

This PR makes the exception explicit in two places, so a future reader doing a "consistency refactor" doesn't accidentally weaken the UX.

Changes

• telegram_bot/handlers/phone_collector.py — module docstring expanded from a single-line #628 note into a full design-exception block referencing Replace custom aiogram FSM with aiogram-dialog (crm_callbacks, phone_collector, demo_handler) #1232 and dialog: document phone collector as justified FSM/router exception (#1232) #2055, with the explicit trade-off and a "drop this exception when..." condition.
• docs/engineering/sdk-registry.md — new bullet at the end of the aiogram-dialog gotchas section calling out phone_collector as the single intentional exception, with cross-references to dialog: migrate CRM quick actions to aiogram-dialog MessageInput + Select (#1232) #2053 and dialog: fold demo handler query input into catalog dialog (#1232) #2054.

This is a docs-only PR — no behaviour change in phone_collector.py.

Verification

uv run python -c 'from telegram_bot.handlers import phone_collector'
  → OK
uv run pytest tests/unit/handlers/test_phone_collector.py \
              tests/unit/handlers/test_phone_crm_integration.py -q
  → 47 passed
uv run python scripts/check_markdown_links.py
  → All relative Markdown links OK.
uvx ruff check telegram_bot/handlers/phone_collector.py
  → All checks passed!

Closes #2055
Parent: #1232