fix: close R268 telemetry coverage and exports

[pcvantol]

Summary

• preserves per-metric CONFLICT/PARTIAL coverage through invocation, attempt, overview and chain projections
• separates monotonic process duration from wall-clock exclusive envelopes without negative or fabricated unassigned time
• applies sum/max/unique/coverage aggregation semantics and privacy-safe event deduplication
• fixes unknown percentage formatting, chain usage and a true interval timeline
• adds complete server-side Markdown and JSON exports for overview and detail/attempt/chain scopes from one canonical snapshot
• releases the coherent change as Engineering Platform 2.3.80

Acceptance paths

• EX-OV-MD: /api/telemetry/export?format=markdown
• EX-OV-JSON: /api/telemetry/export?format=json
• EX-DT-MD: /api/telemetry/YYYY-MM-DD/export?format=markdown&scope=...
• EX-DT-JSON: /api/telemetry/YYYY-MM-DD/export?format=json&scope=...

MD and JSON serialize the same snapshot model. Full exports are server-side and independent of UI preview limits.

Qualification

• full Python suite: 1847 passed, 2 skipped, 264 subtests
• installed-wheel unittest suite: 1849 tests, 1 skipped
• targeted telemetry regressions: 58 passed, 7 subtests
• real isolated HTTP four-export integration: passed with 105 synthetic runs
• coordinated Playwright suite: all 4 shards passed; final targeted export/coverage/timeline set: 5 passed
• en/nl/de/fr/es localization contract: PASS
• 3x2 installed ingress matrix: PASS
• deterministic Genesis/Managed/recovery E2E: PASS
• Quality/Security: PASS; pip-audit 0 known vulnerabilities; npm audit 0; Bandit high 0
• coverage: 84.622486%, no modules below 80%
• production wheel qualification: PASS, SHA-256 b11fb85d3a02245d7e0566347a0531448df146907d8da61bd7f8bf1c1a18c4d1
• isolated installed artifact readback: 2.3.80, telemetry-contract@2.1, telemetry-export@1.0

Safety

Read-only exports do not mutate Missions, submissions, executions, receipts or reports and do not expose raw prompts, replies, shell commands, output dumps, credentials or sensitive paths. Live installation is deliberately deferred until protected delivery completes and the active-execution guard is checked.