docs: documentation overhaul - archive, user guides, env parity (#62)

* docs: archive CLI runner scripts and Windows Docker guide, update web runner scripts

* docs: overhaul README and DOCKER.md, add 10 user guides

- README: Budget Mode section, corrected Further Reading links, theme badge descriptions, diagnostics expansion
- DOCKER.md: Windows path note, Budget Mode + Include/Exclude sections, env table additions
- docs/user_guides/: 10 new feature guides covering budget mode, include/exclude, locks/replace/permalinks, batch build, theme browser, random build, owned cards, partner mechanics, bracket compliance, quick build & skip controls

* fix: map PriceTimeoutError→503, add budget exceptions to status map; update error_handling.md

* docs: env var parity — add missing vars to .env.example and README table

docs/archive/README.md

@@ -0,0 +1,11 @@
+# docs/archive/
+
+Historical snapshots of removed or replaced files. Kept for reference; not part of active documentation.
+
+| File | Archived | Reason |
+|------|----------|--------|
+| `README_2025-10-02.md` | 2025-10-02 | Replaced by full README rewrite |
+| `DOCKER_2025-10-02.md` | 2025-10-02 | Replaced by DOCKER.md rewrite |
+| `WINDOWS_DOCKER_GUIDE_2026-03-23.md` | 2026-03-23 | Removed — ~70% overlap with DOCKER.md. PowerShell quick-start is now covered in the main README and a callout in DOCKER.md. The Docker Desktop GUI walkthrough section was outdated and unmaintainable. |
+| `run-from-dockerhub_2026-03-23.bat` | 2026-03-23 | Removed — launched the interactive CLI mode, which is secondary to the web UI. New users should use `run-web-from-dockerhub.bat` instead. A one-liner covers the CLI case and doesn't need a dedicated script. |
+| `run-from-dockerhub_2026-03-23.sh` | 2026-03-23 | Same reason as the .bat equivalent above. |