deploy: add COPY-into-image tabs, clarify volume ownership, drop mounts

- deploy.md: new 'Getting your files into the image' subsection — a
  multi-tab annotated block (single file / directory / deps-first) showing
  COPY <src> <dest> patterns, plus a warning not to COPY secrets.
- clarify volume ownership: 'Logs and config are ours; the rest is yours' —
  we inject/manage the logs + config host mounts; devs put everything else
  in named volumes Docker owns.
- remove all /srv/mounts: dropped the MOUNTS_DIR volume + env var and every
  mounts reference from the compose block, injected-vars, paths line, and
  checklist. environments.md + index.md mounts mentions cleaned too.

Verified in-browser: COPY tabs switch, volume tip renders, zero mounts refs
remain; mkdocs build --strict clean.

Signed-off-by: disqualifier <dev@disqualifier.me>

docs/environments.md

@@ -68,8 +68,8 @@ happens, depending on where the project runs:
     ```
 
     This is how things run in production — see the [Deploy guide](deploy.md) for the
-    full container standard (uid 1337, mounts, layer caching, and the uv image
-    setup).
+    full container standard (uid 1337, the compose convention, layer caching, and the
+    uv image setup).
 
 !!! tip "Which one?"
     **Local `.venv`** for quick iteration, **Makefile** when you want repeatable