chore: mark skins unsupported, fix stale docs and preview size, prepare 3.4.0 (#580)

* chore: mark skins unsupported, fix stale docs and preview size, prepare 3.4.0

Skins: no current scoreboard plugin builds on src.base_classes, so the only
skin hook (SportsCore._render_game) never runs. The plugin schema endpoint no
longer injects the Visual Skin dropdown, the store hides and refuses
"type": "skin" registry entries, and GET /api/v3/skins reports
supported: false with a message. Stored skin config still loads and saves.
src/skin_system/ and its tests are unchanged apart from the support flag.

Docs: check_plugin.py/render_plugin.py examples use --plugin; document
BasePlugin.get_update_interval() and its interaction with the manifest
update_interval; CLAUDE.md drops the stale template line number and
recommends display_manager.width/height.

Preview size: new src/display_geometry.py holds the size computation and
defaults DisplayManager uses (double-sided applied, chain_length default 2).
The web preview, /display/current, Starlark magnify default, sync handshake
and two dev scripts use it.

Release: __version__ 3.4.0, CHANGELOG 3.4.0 section plus a 3.3.0 tag note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* fix: address CodeRabbit review on #580

- Preview fallbacks (SSE stream and /display/current) use logical_size({})
  (128x32, the shared default) instead of a hard-coded 128x64.
- display_geometry treats a non-mapping display/hardware block as missing,
  so a malformed config.json falls back to defaults instead of raising
  AttributeError (which turned the Starlark render into an HTTP 500).
- Docs: the static update interval falls back manifest -> plugin config
  -> 60s, in both the API reference and the architecture spec.

Not taken: validating double_sided copies against chain_length/parallel.
An orientation Rotate: or U-mapper pixel mapper decides which axis panels
lie on, so the counts would reject working setups (the existing
vertical-split test is one).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* fix(display_geometry): a non-finite hardware size raises ValueError, not OverflowError

CodeRabbit flagged the Starlark magnify default in
_standalone_render_starlark_app for truthy non-mapping display values. That
case was already handled by a9e1bd0b (_display/_hardware treat a non-mapping
block as missing, covered by test_non_mapping_display_config_uses_the_defaults),
and the magnify it produces from the 128x32 defaults is the same as from 64x32.

Checking the same path found one input that still escaped: Python's JSON
parser accepts Infinity, and int(inf) raises OverflowError, which neither the
Starlark path (TypeError, ValueError) nor the preview stream in app.py caught,
so a hand-edited "rows": Infinity returned HTTP 500. physical_size now raises
ValueError for it, matching its documented contract, so every caller's
existing fallback applies. DisplayManager already caught Exception.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

skins/README.md

@@ -1,5 +1,10 @@
 # skins/
 
+> **Not supported yet.** The current scoreboard plugins don't render skins,
+> so a skin placed here and selected in config has no effect, and the web UI
+> and Plugin Store don't offer them. See
+> [docs/SKIN_SYSTEM.md](../docs/SKIN_SYSTEM.md#status-not-supported-yet).
+
 User-installable **visual skins** for the sports scoreboards. Each
 subdirectory is one skin:
 
@@ -10,10 +15,10 @@ skins/<skin-id>/
   preview.png   # optional
 ```
 
-- Install a skin: `git clone <skin repo> skins/<skin-id>` (or via the Plugin
-  Store for registry entries with `"type": "skin"`).
+- Install a skin: `git clone <skin repo> skins/<skin-id>`. The Plugin Store
+  refuses registry entries with `"type": "skin"` while skins don't render.
 - Select it: set `"skin": "<skin-id>"` in the plugin's section of
-  `config/config.json`, or use the web UI's Visual Skin dropdown.
+  `config/config.json`. The web UI no longer shows a Visual Skin dropdown.
 - Build one: start from `example-classic-baseball/` and read
   [docs/CREATING_SKINS.md](../docs/CREATING_SKINS.md). Validate with
   `python scripts/validate_skin.py --skin <skin-id>`.