v1: cleanup, dead code removal, docs update

app.py:
- Move warnings import to top-level imports
- Remove MICRONAS_SECRET env var (undocumented, unnecessary)
- Inline secret key derivation cleanly

CLAUDE.md:
- Remove stale quotas mention
- Add WebDAV, setup.html, favicon to file layout
- Document /etc/micronas/ permissions requirements
- Document <Location> vs <Directory> for WebDAV DAV On

PLANNING.md:
- Mark Phase 5 complete with all shipped items
- Add v1 complete marker and future ideas section

README.md:
- Simplify dev/test section (remove complex hash snippet)
- Fix double blank line

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -5,6 +5,7 @@ import grp
 import hmac
 import shutil
 import hashlib
+import warnings
 import subprocess
 import functools
 from pathlib import Path
@@ -57,13 +58,11 @@ def _save_credentials(user, password):
     _creds['plain'] = ''
     app.secret_key  = hashlib.sha256(h.encode()).hexdigest()
 
-# Derive initial secret key
+# Derive initial secret key from stored credentials
 _secret_src = _creds['hash'] or _creds['plain'] or 'insecure-dev-key'
-app.secret_key = os.environ.get('MICRONAS_SECRET') or \
-    hashlib.sha256(_secret_src.encode()).hexdigest()
+app.secret_key = hashlib.sha256(_secret_src.encode()).hexdigest()
 
 if not _is_configured():
-    import warnings
     warnings.warn('No credentials configured — first-time setup required at /setup', stacklevel=1)