Phase 20: package Linux builds and document release and maintenance workflows

docs/KNOWN_LIMITATIONS.md

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+# Known limitations and qualification boundaries
+
+- Development version 0.1.0, Linux C99/C++17/FLTK, optional JACK. Physical-device
+  playback/capture, human transition listening, independent user acceptance and
+  long-duration device qualification are pending.
+- Fixed 4/4 and constant tempo snapshots; no tempo map, loop transport, plugin
+  latency compensation, limiter, background streaming or multichannel mixer buses.
+- Mono capture/import downmix; stereo track output. Graph ports are mono with
+  independent paired processing. Maximum 64 project graph nodes (256 standalone),
+  64 tracks, 1024 clips/automation points, 4096 scheduled notes, 256 live MIDI
+  events/block, 32 voices, 65536 frames/block. See API headers for exact bounds.
+- WAV samples preload with the memory/format limits in AUDIO_FILES.md. Callback
+  overflow reports/silences; there is no CPU preemption or expensive-plugin rescue.
+- Live MIDI fixed volume/pan/sustain mapping; no controller learn, capture, SMF
+  import, pitch bend, custom-instrument chooser or instrument timbre controls.
+- Native ABI 1 graph nodes are session-only. ABI 2 state is parameter-only. LADSPA
+  supports the documented mono amp/inverter/sine set; no opaque state, native
+  editor, MIDI, true multichannel layout, latency compensation or crash isolation.
+  Automated LADSPA controls use run(1) and can be expensive.
+- GUI loading/compilation is synchronous on the control thread. Timeline grid/
+  zoom/selection and graph positions are session UI state. Undo retains 32 edits
+  plus baseline; allocation failures are reported, not silently hidden. Media is
+  never removed by undo/delete. Broad screen-reader/accessibility testing is pending.
+- Format v7 reads v1–v6 and uses relative local media references. External absolute
+  media/module paths need manual repair after relocation. Saving does not bundle
+  media; missing media stays referenced, missing plugins reject GUI installation.
+  Unknown data is rejected rather than stripped. Post-rename directory-sync errors
+  can report failure even though the complete new document was published.
+- No autosave/session crash restoration, RF64, system service, automatic dependency
+  installation or public signed release. Source/binary archives are local artifacts;
+  binary packages require compatible system libraries. No third-party plugin or
+  dependency binary is bundled. Power-cut durability depends on the filesystem.
+
+See ROADMAP.md, AUDIO_QUALITY.md, CONTROL.md, WORKFLOW.md, PROJECT_FORMAT.md,
+PERFORMANCE.md, PLUGIN_HOSTING.md and RECOVERY.md for tested contracts/evidence.