feat(project): persist bounded per-track effect chains (phase 81)

docs/TRACK_INSERTS.md

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+# Track inserts
+
+The sequencer's **Create** dropdown groups track creation, WAV import and
+instrument loading. **View → Track inspector** opens the optional inspector;
+it is hidden when the application starts to leave more room for editing.
+
+Project format 17 stores up to eight effect slots per track, their order,
+bypass, wet amount and chain output gain. Formats 1–16 read with empty chains.
+Metadata load, clone and history never open executable plugin modules. Track
+move, duplicate and removal retain the association with stable track IDs.
+Nonempty bus chains are rejected. The model accepts mono effect specifications
+for LADSPA, VST2, VST3, CLAP and internal effects; this alone does not establish
+that a third-party binary is compatible with the host.
+
+The chain API is declared in `xtc_plugin.h`. Setter errors preserve the old
+chain; plugin identity and layout are checked when preparing playback.