docs: update comments and README to reflect current feature set

- Refresh app.py module and route docstrings for runtime settings,
  MP3 tagging, rate limiting, revision workflow, and admin actions.
- Clarify config.py and models.py comments.
- Update template comments/CSS for dashboard filters, request detail,
  player page, and settings page.
- Rewrite README.md with current features, status flow, file layout,
  deployment variables, and troubleshooting.
- Refresh REVIEW.md quick-reference.
- Add MAX_REVISIONS to docker-compose.yml environment list.
- Expand requirements.txt comment coverage.

No version history or changelog included.

templates/admin/request.html

@@ -9,10 +9,10 @@
       Single-request admin detail page.
       Sections:
         1. Customer info (with revisions note if any)
-        2. Generate Suno prompt
-        3. Upload Songs
-        4. Notify Customer
-        5. Payment & Delivery
+        2. Generate and save Suno prompt
+        3. Upload Version A and Version B MP3s
+        4. Send preview email with private player link
+        5. Mark paid and deliver selected MP3(s)
     */
     body{
       font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,sans-serif;
@@ -154,7 +154,7 @@
 
     <!-- Section 2: Generate Suno prompt -->
     <div class="section">
-      <h2>1. Generate Suno Prompt</h2>
+      <h2>1. Generate & Save Suno Prompt</h2>
 
       <button type="button" onclick="copyPromptForHermes()">Copy customer info for Hermes</button>
       <p class="copy-hint">Paste Hermes' Title, Style, and Lyrics directly into the fields below, then save.</p>