feat: clipboard export, persisted bearing, and poster presets

[ehabmansour1]

Summary

Three additive features that improve the poster authoring loop:

• Copy poster to clipboard — new "Copy" button (teal) in both desktop flyout and mobile export modal. Uses navigator.clipboard.write with ClipboardItem to put a PNG of the composited poster on the system clipboard.
• Persisted map bearing — bearing is now a PosterForm field, so map rotation survives across interactions, syncs through MapPreview alongside center/zoom (with a new MAP_BEARING_SYNC_EPSILON), and is captured by presets. Local mapBearing state in PreviewPanel was removed.
• Poster presets — new vertical slice under src/features/presets/ (domain / infrastructure / application / ui). Saves up to 20 named configurations (PosterForm + customColors) to localStorage under a stable key (terraink:presets), no TTL. Surfaces as a new "Presets" accordion section in SettingsPanel.

Each feature is in its own commit so they can be reviewed (or reverted) independently.

Architecture notes

• Clipboard exporter follows the existing infrastructure pattern: new file in features/export/infrastructure/, re-exported from features/export/infrastructure/index.ts and core/services.ts. Hook handles dispatch of the new "clipboard" ExportFormat branch inside useExport.exportPoster.
• Bearing change is the cleanest way to make rotation work with presets — without it, loading a preset would silently lose the user's chosen orientation. Export already reads bearing from the live map instance, so no changes were needed in mapExporter.ts / exportUtils.ts.
• Presets storage deliberately avoids localStorageCache because that adapter enforces a TTL and namespaces by APP_VERSION (presets would be wiped on every release). Uses a plain stable key instead, mirroring how custom marker icons use IndexedDB for durable user data.
• Loading a preset dispatches SET_THEME (resets customColors) → SET_FORM_FIELDS → per-color SET_COLOR, reusing existing reducer actions instead of adding a new LOAD_PRESET action.

Test plan

• Click the new Copy button (desktop flyout / mobile modal) → poster lands on clipboard, can be pasted into an image editor
• Verify copy works while flyout stays open during the in-flight export
• Rotate the map, lock it, unlock again → bearing is preserved (previously reset to 0)
• Rotate, then recenter → bearing resets to 0 (existing recenter behavior preserved)
• Save a preset with a custom name, change theme/location/bearing/colors, click the preset → all fields restored including bearing and custom colors
• Save more than 20 presets → oldest entries are evicted (cap = 20)
• Delete a preset → removed from list and localStorage
• Reload the page → presets persist
• bun run build passes (verified locally)

Notes

• Three pre-existing TypeScript errors in pngExporter.ts, StartupLocationModal.tsx, and typography.ts are unrelated to this PR and untouched.
• Firefox does not yet support image writes via the Clipboard API; the exporter throws a clear error message in that case.

[yousifamanuel]

@ehabmansour1 thank you for your contribution again!

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