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>

docs/README.md

@@ -56,8 +56,8 @@ Going deeper:
 - [ADVANCED_FEATURES.md](ADVANCED_FEATURES.md) — Vegas scroll, on-demand display,
   cache management, background services, permissions
 - [FONT_MANAGER.md](FONT_MANAGER.md) — font system
-- [SKIN_SYSTEM.md](SKIN_SYSTEM.md) — skin architecture for sports scoreboards
-- [CREATING_SKINS.md](CREATING_SKINS.md) — writing and validating a skin
+- [SKIN_SYSTEM.md](SKIN_SYSTEM.md) — skin architecture for sports scoreboards (not supported yet: current scoreboards don't render skins)
+- [CREATING_SKINS.md](CREATING_SKINS.md) — writing and validating a skin (same caveat)
 
 ## Reference