Add deployment guide for speakers app removal

Documents the complete deployment procedure including:
- Pre-deployment checklist
- Step-by-step migration instructions
- Rollback procedure
- Troubleshooting guide
- Post-deployment cleanup

This guide should be followed when deploying PR #161 to production.

Author: matrixise

MIGRATION_DEPLOYMENT.md

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+# Deployment Guide: Removing Speakers App
+
+This guide explains how to safely deploy PR #161 which removes the speakers app from the Python Ireland website.
+
+## Overview
+
+PR #161 removes the entire `speakers` Django app and all associated code. A database migration has been created to cleanly drop the speakers tables from production.
+
+## Pre-requisites
+
+✅ All speaker/session records have been deleted from production database
+✅ No Wagtail pages of type SpeakersPage or TalksPage exist in production
+✅ Recent database backup exists
+
+## Deployment Steps
+
+### Step 1: Create a Backup
+
+**CRITICAL**: Always backup before running destructive migrations.
+
+```bash
+# Create a fresh backup
+task heroku:database:run-backup
+
+# Verify the backup was created
+task heroku:database:backups
+```
+
+### Step 2: Merge the PR
+
+Merge PR #161 into master branch:
+
+```bash
+# Via GitHub CLI
+gh pr merge 161 --squash --delete-branch
+
+# Or via GitHub web interface
+```
+
+### Step 3: Deploy to Heroku
+
+The deployment will happen automatically if auto-deploy is configured, or manually:
+
+```bash
+# Pull latest master
+git checkout master
+git pull origin master
+
+# Push to Heroku (if manual deployment)
+git push heroku master
+```
+
+### Step 4: Run the Migration
+
+The migration will run automatically during Heroku release phase. If you need to run it manually:
+
+```bash
+# Run migrations on Heroku
+task heroku:migrate
+
+# Or directly:
+heroku run python pythonie/manage.py migrate --settings=pythonie.settings.production
+```
+
+The migration `0010_remove_speakers_tables` will:
+- Drop `speakers_session_speakers` (M2M table)
+- Drop `speakers_session`
+- Drop `speakers_speaker`
+- Drop `speakers_room`
+- Drop `speakers_talkspage`
+- Drop `speakers_speakerspage`
+
+### Step 5: Verify Deployment
+
+```bash
+# Check application logs
+task heroku:logs
+
+# Verify app is running
+heroku ps
+
+# Test the website
+curl -I https://python.ie
+
+# Verify migration ran
+heroku run python pythonie/manage.py showmigrations core --settings=pythonie.settings.production
+```
+
+You should see `[X] 0010_remove_speakers_tables` in the output.
+
+### Step 6: Verify Tables Were Dropped
+
+```bash
+# Connect to production database
+heroku pg:psql
+
+# Check for speakers tables (should return no rows)
+\dt speakers_*
+
+# Exit psql
+\q
+```
+
+## Rollback Procedure
+
+⚠️ **WARNING**: The migration is IRREVERSIBLE by design.
+
+If you need to rollback:
+
+1. **Restore from backup**:
+   ```bash
+   # List backups
+   heroku pg:backups
+
+   # Restore from backup (replace b001 with your backup ID)
+   heroku pg:backups:restore b001 DATABASE_URL
+   ```
+
+2. **Revert the code**:
+   ```bash
+   # Rollback Heroku release
+   task heroku:rollback
+
+   # Or force push previous commit
+   git checkout <previous-commit-sha>
+   git push heroku HEAD:master --force
+   ```
+
+## Troubleshooting
+
+### Migration fails with "table does not exist"
+
+This is OK if the tables were already manually dropped. The migration uses `DROP TABLE IF EXISTS` so it won't error.
+
+### Application won't start after deployment
+
+Check logs for the specific error:
+```bash
+task heroku:logs
+```
+
+Common issues:
+- Missing environment variable
+- Database connection issue
+- Code import error
+
+### Need to verify migration status
+
+```bash
+# Show all migrations and their status
+heroku run python pythonie/manage.py showmigrations --settings=pythonie.settings.production
+```
+
+## Post-Deployment Cleanup
+
+After successful deployment, clean up your local environment:
+
+```bash
+# Remove the worktree
+cd /Users/stephane/src/PythonIreland/website
+git worktree remove /Users/stephane/src/PythonIreland/pythonie-remove-speakers
+
+# Delete local branch
+git branch -d remove-speakers
+
+# Verify worktrees
+git worktree list
+```
+
+## Migration Details
+
+**File**: `pythonie/core/migrations/0010_remove_speakers_tables.py`
+
+**What it does**:
+- Uses raw SQL to drop speakers tables
+- Handles CASCADE for foreign key constraints
+- Drops tables in correct dependency order
+- Is irreversible (raises RuntimeError on reverse)
+
+**Why in core app**:
+The speakers app has been completely removed from the codebase, so the migration must live in another app (core was chosen as it's the base app).
+
+## Notes
+
+- This migration does NOT delete data - data should be deleted before running the migration
+- The migration is idempotent - safe to run multiple times
+- All table drops use CASCADE to handle foreign keys
+- The migration cannot be reversed - backup is essential
+
+## Success Criteria
+
+✅ Application deploys successfully
+✅ No errors in Heroku logs
+✅ Website loads at https://python.ie
+✅ Migration 0010_remove_speakers_tables shows as applied
+✅ No speakers_* tables exist in database
+✅ Admin interface works correctly
+
+## Support
+
+If you encounter issues during deployment:
+
+1. Check Heroku logs: `task heroku:logs`
+2. Verify migration status: `heroku run python pythonie/manage.py showmigrations`
+3. Restore from backup if needed
+4. Contact the development team
+
+---
+
+**Created**: 2026-01-11
+**PR**: #161
+**Migration**: `core.0010_remove_speakers_tables`