Fountain import: frontend wiring (menu, Open dialog, Import as Episode, per-episode export)

[stultus]

Part of #184 (Fountain import).

What

Wire the Rust Fountain parser into the frontend and add the user-facing entry points.

Surface area

Tauri commands (Rust → TS bridge)

• import_fountain_as_film(path: String) -> Result<ScreenplayDocument, String>
• import_fountain_as_episode(path: String, current_doc: ScreenplayDocument) -> Result<ScreenplayDocument, String> — returns the mutated Series document with the new episode appended, the active episode pointer updated.
• Both return alongside an import summary (counts of dropped boneyards, absorbed sections, etc.) so the frontend can show a toast.

Native menu

• File → Import Fountain... — always creates a new untitled Film. Goes through the dirty-state guard (documentStore.confirmIfDirty()).
• File → Import Fountain as Episode... — only enabled when document.type === \"series\". Appends new episode; switches active episode to it.

Open dialog

• Existing Open accepts .screenplay. Extend to also accept .fountain and route to import_fountain_as_film based on extension.
• Same dirty-state guard applies.

Per-episode Fountain export (Series only)

• Add a "Per episode" toggle to the Export modal, visible only when format = Fountain (and plain text — same logic, smaller win) and project is a Series.
• When checked, the directory picker replaces the file picker. Output: {NN}-{slug(episode.title)}.fountain for each episode.

Import summary toast

After a successful import, show a small toast: Imported \"Filename.fountain\" — 12 scenes, 3 boneyards dropped. Reuse the UpdateToast styling pattern.

Tasks

• Two Tauri commands in src-tauri/src/commands/
• File menu items in src-tauri/src/lib.rs (native menu) — mirroring the existing custom-quit pattern
• Frontend menu-event handlers in src/routes/+page.svelte
• Open dialog extension filter update
• Per-episode export branch in ExportModal.svelte + a per-episode export Tauri command
• Import summary toast component (or reuse a generic toast)
• Remove Fountain import from the "Deferred" list in .claude/CLAUDE.md

Out of scope

• Drag-and-drop a .fountain file onto the window (separate small enhancement)

[stultus]

Landed in 07dd628. Three entry points wired (File menu, ⌘O Open dialog, Command palette), ImportSummaryToast shows transformations/drops/warnings, per-episode Fountain export added to ExportModal for series projects. End-to-end testing requires the actual Tauri desktop build (cargo tauri dev) — the menu items + native dialogs aren't reachable from the browser dev server. Closing once #188 (export round-trip with forcing rules) lands.

[stultus]

Landed in 07dd628 (frontend wiring + per-episode export). Closing — end-to-end testing requires the Tauri dev build for the menu items + native dialogs.