refactor: make all scripts multi-project via env vars

Replace hardcoded harb references across the entire codebase:
- HARB_REPO_ROOT → PROJECT_REPO_ROOT (with deprecated alias)
- Derive PROJECT_NAME from CODEBERG_REPO slug
- Add PRIMARY_BRANCH (master/main), WOODPECKER_REPO_ID env vars
- Parameterize worktree prefixes, docker container names, branch refs
- Genericize agent prompts (gardener, factory supervisor)
- Update best-practices docs to use $-vars, prefix harb lessons

All project-specific values now flow from .env → lib/env.sh → scripts.
Backward-compatible: existing harb setups work without .env changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

factory/best-practices/codeberg.md

@@ -10,8 +10,8 @@ Codeberg rate-limits SSH and HTTPS clones. Symptoms:
 - **Do NOT retrigger** during a rate-limit storm. Wait 10-15 minutes.
 - Check if multiple pipelines failed on `git` step recently:
   ```bash
-  wpdb -c "SELECT number, status, to_timestamp(started) FROM pipelines WHERE repo_id=2 AND status='failure' ORDER BY number DESC LIMIT 5;"
-  wpdb -c "SELECT s.name, s.exit_code FROM steps s JOIN pipelines p ON s.pipeline_id=p.id WHERE p.number=<N> AND p.repo_id=2 AND s.state='failure';"
+  wpdb -c "SELECT number, status, to_timestamp(started) FROM pipelines WHERE repo_id=$WOODPECKER_REPO_ID AND status='failure' ORDER BY number DESC LIMIT 5;"
+  wpdb -c "SELECT s.name, s.exit_code FROM steps s JOIN pipelines p ON s.pipeline_id=p.id WHERE p.number=<N> AND p.repo_id=$WOODPECKER_REPO_ID AND s.state='failure';"
   ```
 - If multiple `git` failures with exit 128 in the last 15 min → it's rate limiting. Wait.
 - Only retrigger after 15+ minutes of no CI activity.