feat(editor): localised analyzer/strip/run messages + monospace font fallback

Closes operator-reported issues around the text-tab font and
the English-only run + diagnostic surfaces.

  - **Real monospace everywhere**. The package never bundled
    JetBrains Mono as an asset (it relied on Studio's
    google_fonts pre-load), so a host that doesn't ship the
    font saw the YAML editor render in the system proportional
    default. New _monoTextStyle() pins fontFamilyFallback to a
    cross-platform monospace chain (Menlo / Consolas / Courier
    New / monospace) so the editor stays a grid in every host.
    Applied to the code field, gutter, diagnostic strip,
    issue rows, hover card, fix buttons, and the run tab's
    error box.

  - **Locale-aware analyzer messages**. New AnalyzerStrings
    adapter holds every string the analyzer emits, with an
    .english default + an .from(FlowEditorStrings) factory.
    FlowYamlCodeController.setCapabilityProviders takes the
    strings; FlowEditorPage wires them from the active locale.
    The analyzer's 'Unknown capability', 'Did you mean',
    'Not in the store — install locally with fai install
    --link', 'Unknown input/output type', YAML parse errors,
    and every quick-fix label (Install / Add source / Use /
    Change to) now flip to DE when the editor's locale is DE.

  - **Localised run + diagnostic chrome**. The bottom strip's
    'No issues', '2 errors · 1 warning', 'Copy all'; the
    issue row's L-prefix + Copy tooltip; the hover card's
    L-prefix + Copy tooltip; the run-block tooltip + inline
    message ('2 Fehler verhindern den Lauf · siehe
    Diagnose-Leiste unten'); the step-row 'awaiting approval'
    suffix; the CopyableErrorBox's Copy / Copied tooltip —
    all now flow through FlowEditorStrings.

Bumped to 0.20.0.

Signed-off-by: flemming-it <sf@flemming.it>

pubspec.yaml

@@ -1,6 +1,6 @@
 name: fai_studio_flow_editor
 description: Swappable inline YAML editor for F∆I Studio flows.
-version: 0.19.0
+version: 0.20.0
 publish_to: 'none'
 repository: https://git.flemming.ai/fai/studio-flow-editor