ability to only run specified Stream Decks instead of all attached decks - #227

Brings src/windows/** from 254 mypy errors to 0. Type-only apart from the
genuine defects below, each of which mypy surfaced.

Bugs fixed (behaviour changes):
- AssetManager/CustomAssets/Chooser.py: gl.asset_manager.set_cursor_from_name
  was called unguarded, but AssetManager.on_close nulls gl.asset_manager -- a
  drop or file-dialog callback landing after the window closed raised
  AttributeError. Guarded; the files are still added.
- mainWindow.py: get_active_page() returned gl.page_manager.dummy_page, an
  attribute that exists nowhere, so the no-deck-selected path raised
  AttributeError. Returns None (the widened contract) instead.
- ActionMissing/OutdatedActionRow.py: passed coords= to a MissingRow that
  takes identifier=, so every outdated-action row raised TypeError. Signature
  realigned with the sibling MissingActionButtonRow and its call site.
- Sidebar/Sidebar.py: KeyEditorKeyBox.load_for_key called
  ActionManager.load_for_coords, which lives on ActionGroup -> AttributeError.
- ActionManager.py: ActionRow.update_comment wrote to a comment_row that has
  never existed (comment_label does). set_label_toggled referenced an
  on_allow_label_toggled handler on no class; disabled alongside its
  already-commented call site.
- ActionConfigurator.py: select_event dereferenced a None event_assigner when
  the model's first item was not the "None" entry.
- StreamDeckUI/code_conv.py: a bare `# type: ignore` hid an undefined
  _DELAY_KEYSYM, so any imported hotkey with a delay token raised NameError
  into the importer's except and silently dropped the whole hotkey. Delay
  tokens are now rejected explicitly.
- Store/InfoPage.py: set_stargazer drove a row commented out in build();
  disabled with it.
- Settings/Settings.py: CustomContentEntry assigned url/branch strings that
  the EntryRow widgets overwrote two statements later; dead stores removed.

Contract corrections: MainWindow.get_active_controller/get_active_page,
DeckStack.remove_page/get_page_attributes, PageSelector.sort_func,
OnboardingWindow.set_button_status, Store preview setters and
ImageEditor.update_values (annotated KeyLabel, handed an ImageLayout) all
declared types their bodies contradict.

Forwarded guards: ActionChooser's get_arrow_image() call sites (MR 2) and
PluginSettingsPage's ActionRow title (MR 3).

24 pinned ignores (12 gi stub, 6 late-init, 6 cross-MR forwards), 1 bare
ignore removed. Total mypy errors 949 -> 679; no new out-of-scope errors
(StoreBackend drops 16 via the StoreData widening MR 6 asked for).

Review round on the previous commit.

10th defect, directly under the earlier edit: EventAssignerUI.
change_assignment_for_event called self.action.set_event_assignments, which
exists on no class (ActionCore only has the singular set_event_assignment,
ActionCore.py:591). Its one call site sat after an unconditional return in
EventAssignerRow.on_changed, so the whole tail was dead -- and the comment
added last round ("the persisted map is keyed and valued by the events'
string names") was wrong twice over: persisted VALUES are event_assigner.id
strings (Page.py:572), not event names. Deleted the dead method and the dead
tail of on_changed instead of type-annotating fiction; the live part of
on_changed (get_event_assigner_by_id -> set_event_assignment) is untouched.

Guard asymmetry corrected: last round guarded gl.app in the DEAD _on_close
while the live on_close (:83) still dereferenced gl.app unguarded for
GLib.idle_add(gl.app.on_quit). gl.app is honestly Optional, so the live path
is now guarded too.

Honesty corrections to the previous commit message:
- Sidebar.py KeyEditorKeyBox.load_for_key: the load_for_coords ->
  load_for_identifier fix is correct, but KeyEditorKeyBox is instantiated
  nowhere, so this was dead code, not a live AttributeError. The same method
  also passes key.coords where an InputIdentifier is expected (hidden by an
  unannotated return type) -- left for the residual sweep.
- Store/Icons/IconPage.py: the guarded get_custom_translation block is dead
  -- the next line unconditionally overwrites `description` from
  short_description/description. Pre-existing; the guard is still correct for
  the day that line goes.
- The three FlowBox super().__init__(base_class=...) -> positional changes
  are no-ops today: every construction goes through FLOW_BOX_CLASS(preview,
  chooser) with an empty *args.

Gates unchanged: src/windows/** 0 errors, total 679, 24 pinned ignores,
ruff clean, harness 174/174.

…roller#227)

Rebased onto gitlab/main (86db4f9, MRs StreamController#222/StreamController#223/StreamController#225/StreamController#226 landed). Eleven
in-scope errors appeared, all from StreamController#225's honest widening; re-zeroed.

Absorbed (11):
- LabelEditor.py (10) -- KeyLabel.text/color/outline_width/outline_color/
  alignment/font_name/font_size/style/font_weight are all `| None` now.
  _update_values_locked treats an unset text as "", and the four LabelRow
  setters take `| None` and no-op rather than being handed a None (which
  color_values_to_gdk / set_value would have raised on). The font
  description needs all four properties, so an incompletely composed label
  leaves the chooser alone instead of calling Pango with None.
- ImageEditor.py (1) -- ImageLayout.size is `| None`; the spinner keeps its
  value when unset instead of evaluating None*100.

Stale ignores removed (4): StreamController#225 fixed both root causes this branch forwarded,
so the two color_values_to_gdk arg-type ignores in LabelEditor and the two
InputIdentifier.Events attr-defined ignores in ActionConfigurator are gone.
Verified with a --warn-unused-ignores diagnostic run: no stale ignores remain
in src/windows (config untouched).

Ignores: 24 -> 20 (12 gi stub, 6 late-init, 2 cross-MR).

Both surviving cross-MR forwards outlived StreamController#226, which zeroed those files
without widening the two signatures (their only offending callers live in
src/windows, so StreamController#226 never saw the errors) -- for the residual sweep:
- PageManagerBackend.set_default_page:309 `path: str`, but None is the
  documented "clear the default" value.
- AssetManagerBackend.add_custom_media_set_by_ui:333 `path: str`, whose first
  branch is `if path is None and url is not None`.

Gates on the rebased tree: src/windows/** 0 errors, total 228 (all in
DeckController.py 227 + ActionCore.py 1, i.e. StreamController#224's scope), ruff clean,
harness 175/175.

types(7/8): windows/ to zero mypy errors

Closes StreamController#227

See merge request naz/Deckard!116