Implement ChordPro, LRC, and accessible PDF/print exports

[qisoft]

Outcome

Deliver deterministic compatibility projections with explicit omission/degradation reporting.

Scope

• ChordPro lead-sheet projection with chords, sections, grid, meter/key/tempo/capo and diagrams
• line-onset UTF-8 LRC with monotonic validated timings only
• self-contained tagged PDF/print with embedded fonts, logical reading order and diagram alternatives
• automatic inclusion of selected lyrics with provenance/notices and no legal gate

Acceptance gates

• unsupported rich chords remain visible and are never silently simplified
• unmatched/unsafe LRC lines are omitted and reported without fabricated timestamps
• timing/confidence/identity/mismatch losses are recorded in the Receipt
• PDF/print layout is deterministic and accessible without claiming untested PDF/A or PDF/UA

Planning authority

• https://github.com/qisoft/open-chords/blob/7212b97/docs/specification/open-chords-v1.md
• https://github.com/qisoft/open-chords/blob/feature/implementation-plan/docs/planning/open-chords-v1-implementation-plan.md

Constraints

• Implement through tests at the module interface and the named cross-process/packaged seams.
• Preserve all normative security, privacy, provenance, nondestructive-state, accessibility, and no-unmeasured-claim rules.
• Native GitHub blockers define readiness; do not bypass them by weakening the acceptance gate.

[qisoft]

PR #94 merged at 80cdc7c7dc3a5f01bac140213e1763990d1bf974. ChordPro, safe line-onset LRC, tagged deterministic PDF, and durable loss-bearing Export Receipts are implemented. CodeRabbit's latest incremental review covered 61bb1ce and generated no actionable comments; the earlier wording finding is verified and resolved. All four current-head checks passed in CI run 37607842444, including installed macOS arm64 and Windows x64 checks.

Evidence limits: renderer CI exercises real export IPC with a substituted native-picker response. Installed CI reopens all format Receipts. This does not establish actual native save-dialog behavior or native screen-reader acceptance. The native blockers #41 and #48 remain authoritative; this issue stays open pending those gates. Implementation details and projection limits are in docs/development/compatibility-exports.md.