add specs and tasks for registration-confirmation-email

specs/registration-notifications/spec.md:
- MODIFIED: parent confirmation email sent on completion (alongside admin)
- Bilingual body (de/en), QR-bill embedded inline, plain-text fallback
- Language persisted as metadata.language in registration record

tasks.md:
- 6 sections: qrbill dep, language persistence, notify_parent() impl,
  wire into both completion sites (email agent + chat), tests, smoke test

https://claude.ai/code/session_01LjjK7RjKVnC8bETtccfgna

openspec/changes/registration-confirmation-email/specs/registration-notifications/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Notify parent on completed registration
+The system SHALL send an HTML confirmation email to the parent immediately after a registration is completed and stored.
+
+#### Scenario: Confirmation sent to parent email
+- **WHEN** a registration is completed
+- **THEN** the system SHALL send a confirmation email to the address in `parentGuardian.email`
+
+#### Scenario: Confirmation sent before or alongside admin notification
+- **WHEN** a registration is completed
+- **THEN** both the admin notification and the parent confirmation SHALL be dispatched in the same completion event; failure of either SHALL be logged but SHALL NOT block the other or fail the registration
+
+#### Scenario: No confirmation for incomplete registration
+- **WHEN** a registration is not yet complete (any required field missing)
+- **THEN** no confirmation email SHALL be sent to the parent
+
+---
+
+### Requirement: Confirmation email contains full registration summary
+The confirmation email SHALL include a summary of all registration data the parent submitted.
+
+#### Scenario: All required fields present in confirmation
+- **WHEN** the confirmation email is sent
+- **THEN** it SHALL include child name, date of birth, special needs, selected playgroup type(s), selected days, parent/guardian contact details, and emergency contact
+
+#### Scenario: Monthly fee shown as informational text
+- **WHEN** the confirmation email is sent
+- **THEN** it SHALL display the calculated monthly subscription fee as informational text (not a payment request)
+
+---
+
+### Requirement: Confirmation email contains payment instructions for registration fee
+The confirmation email SHALL include instructions for paying the one-time CHF 80 registration fee.
+
+#### Scenario: IBAN and payee shown as text
+- **WHEN** the confirmation email is sent
+- **THEN** it SHALL display the payee name, IBAN, and amount in plain text so the parent can pay manually if the QR code is not rendered
+
+#### Scenario: Swiss QR-bill embedded inline
+- **WHEN** the confirmation email is sent
+- **THEN** it SHALL include a Swiss QR-bill image (per SIX Group standard) embedded inline as a `Content-ID` referenced image within the HTML part
+- **AND** the QR-bill SHALL encode: IBAN `CH14 0900 0000 4930 8018 8`, payee Familienverein Fällanden Spielgruppen (Huebwisstrase 5, 8117 Fällanden), amount CHF 80.00, currency CHF, reference type NON
+
+#### Scenario: QR-bill fallback for non-HTML clients
+- **WHEN** a parent's email client does not render HTML
+- **THEN** the plain-text part SHALL include the IBAN and payee details in full so payment is still possible without the QR code
+
+---
+
+### Requirement: Confirmation email language matches parent's detected language
+The confirmation email body SHALL be rendered in the language detected during the conversation.
+
+#### Scenario: German parent receives German confirmation
+- **WHEN** the conversation language is `"de"`
+- **THEN** the confirmation email body SHALL be in German
+
+#### Scenario: English-speaking parent receives English confirmation
+- **WHEN** the conversation language is `"en"`
+- **THEN** the confirmation email body SHALL be in English
+
+#### Scenario: Unknown language falls back to German
+- **WHEN** the stored language value is not `"de"` or `"en"`
+- **THEN** the confirmation email SHALL be sent in German
+
+#### Scenario: QR-bill slip labels are not translated
+- **WHEN** the confirmation email is rendered in any language
+- **THEN** the Swiss QR-bill payment slip labels SHALL remain in German (per SIX Group standard; the slip is internationally recognisable without translation)
+
+---
+
+### Requirement: Parent's conversation language is persisted in the registration record
+The language detected during the parent's conversation SHALL be stored in the completed registration record.
+
+#### Scenario: Language written to registration record
+- **WHEN** a registration is stored
+- **THEN** the JSON record SHALL include a `metadata.language` field containing the detected language code (`"de"` or `"en"`)
+
+#### Scenario: Language defaults to German when not detected
+- **WHEN** no language was explicitly detected during the conversation
+- **THEN** `metadata.language` SHALL be `"de"`