feat(ui): add generate tab builder with prompt/lyrics/duration/vocal mode

tooltips.py

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+"""Centralised tooltip / `info=` strings — single source of truth."""
+
+GENERATE_PROMPT = "Describe the song. Genre, instruments, tempo, mood."
+GENERATE_LYRICS = "Use [verse] [chorus] [bridge] tags. Open the Lyrics tab to draft with Qwen 2.5."
+GENERATE_DURATION = "Output length in seconds. Longer outputs cost more compute."
+GENERATE_VOCAL = "With vocals: full song. Instrumental: no singing, just music."

ui.py

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+"""Per-tab Gradio component builders + shared output panel.
+
+Each builder returns a dict of components keyed by purpose so app.py wires
+events without depending on Gradio's positional return order.
+
+NOTE: builders DO NOT instantiate the surrounding gr.Group / pane — they
+ONLY build the form + output components inside it. app.py wraps the
+result in pane_generate / pane_cover / etc.
+"""
+
+from __future__ import annotations
+
+import gradio as gr
+
+import tooltips
+
+
+def build_generate_tab() -> dict[str, gr.components.Component]:
+    """Generate tab body: 2-column row (form left, output right).
+
+    LoRA / Advanced / LM-planner / DCW accordions are deferred to
+    M2-M4 and will be added by extending this builder.
+    """
+    components: dict[str, gr.components.Component] = {}
+
+    with gr.Row():
+        # --- FORM column (left, ~60% width) ---
+        with gr.Column(scale=13):
+            components["prompt"] = gr.Textbox(
+                label="Style prompt",
+                placeholder="psytrance, rolling triplet bassline, acid squelch, metallic leads",
+                lines=2,
+                info=tooltips.GENERATE_PROMPT,
+            )
+            components["lyrics"] = gr.Textbox(
+                label="Lyrics",
+                placeholder="[intro] atmospheric pads\n[verse] ...",
+                lines=6,
+                info=tooltips.GENERATE_LYRICS,
+            )
+            with gr.Row():
+                components["duration_s"] = gr.Slider(
+                    minimum=5,
+                    maximum=240,
+                    step=5,
+                    value=30,
+                    label="Duration (s)",
+                    info=tooltips.GENERATE_DURATION,
+                )
+                components["instrumental"] = gr.Radio(
+                    choices=["With vocals", "Instrumental"],
+                    value="With vocals",
+                    label="Vocal mode",
+                    info=tooltips.GENERATE_VOCAL,
+                )
+            components["generate_btn"] = gr.Button(
+                "▶ Generate",
+                variant="primary",
+            )
+
+        # --- OUTPUT column (right, ~40% width) ---
+        with gr.Column(scale=10):
+            components["output_audio"] = gr.Audio(
+                label="Output",
+                type="filepath",
+                interactive=False,
+                show_download_button=True,
+            )
+            components["output_meta"] = gr.Code(
+                label="Metadata",
+                language="json",
+            )
+
+    return components