feat: Excel template export with meeting number auto-generation

- Add meeting_number field (M-YYYYMMDD-XX format) with auto-generation
- Refactor Excel export to use cell coordinates instead of placeholders
- Export files saved to backend/record/ directory with meeting number filename
- Add database migration for meeting_number column
- Add start.sh script for managing frontend/backend/sidecar services
- Update OpenSpec documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2025-12-11-update-excel-template-export/specs/meeting-management/spec.md

@@ -0,0 +1,35 @@
+## MODIFIED Requirements
+
+### Requirement: Create Meeting
+The system SHALL allow users to create meetings with required metadata and auto-generated meeting number.
+
+#### Scenario: Create meeting with all fields
+- **WHEN** user submits POST /api/meetings with subject, meeting_time, chairperson, location, recorder, attendees
+- **THEN** a new meeting record SHALL be created with auto-generated UUID, meeting_number, and the meeting data SHALL be returned
+
+#### Scenario: Create meeting with missing required fields
+- **WHEN** user submits POST /api/meetings without subject or meeting_time
+- **THEN** the server SHALL return HTTP 400 with validation error details
+
+#### Scenario: Recorder defaults to current user
+- **WHEN** user creates meeting without specifying recorder
+- **THEN** the recorder field SHALL default to the logged-in user's email
+
+#### Scenario: Auto-generate meeting number
+- **WHEN** a new meeting is created
+- **THEN** meeting_number SHALL be auto-generated in format M-YYYYMMDD-XX
+
+### Requirement: System Code Generation
+The system SHALL auto-generate unique system codes for meetings, conclusions, and action items.
+
+#### Scenario: Generate meeting number
+- **WHEN** a meeting is created on 2025-12-10
+- **THEN** the meeting_number SHALL follow format M-20251210-XX where XX is sequence number
+
+#### Scenario: Generate conclusion code
+- **WHEN** a conclusion is created for a meeting on 2025-12-10
+- **THEN** the system_code SHALL follow format C-20251210-XX where XX is sequence number
+
+#### Scenario: Generate action item code
+- **WHEN** an action item is created for a meeting on 2025-12-10
+- **THEN** the system_code SHALL follow format A-20251210-XX where XX is sequence number