feat(sessions): export sessions to Markdown/QMD

[web3blind]

Summary

• add hermes sessions export-md for Markdown/QMD session exports
• support filtered bulk export, dry-run previews, logical compression-lineage export, and manifest JSONL with SHA-256 metadata
• add guarded single-session --delete-after-verified --yes flow that verifies the export before deletion
• document the new workflow and add regression coverage for formatter, CLI, and session-store helpers

Verification

• python3 -m py_compile hermes_cli/session_export_md.py hermes_cli/main.py hermes_state.py
• scripts/run_tests.sh tests/hermes_state/test_session_md_export.py tests/hermes_cli/test_session_export_md.py tests/hermes_cli/test_sessions_export_md_cli.py tests/hermes_cli/test_sessions_delete.py tests/test_hermes_state.py — 349 passed, 0 failed
• git diff --check
• smoke-tested read-only logical export against a local session; smoke-tested delete-after-verified only against a temporary HERMES_HOME/state.db

[web3blind]

Context / rationale:

This PR adds a readable Markdown/QMD export path for Hermes sessions as a safer alternative to going straight from SQLite retention pressure to destructive pruning.

Why this matters:

• Session history is long-term user memory, not just disposable logs.
• The existing JSONL export is good for machines, but awkward for humans, Obsidian, grep/rg, and RAG-style recall.
• archive is intentionally a SQLite soft-archive, not a portable external backup.
• A verified file export gives users a safer workflow: materialize sessions first, inspect/search them outside SQLite, then only delete a specifically named session when the export verifies.

Safety choices in this PR:

• Bulk Markdown/QMD export is read-only and requires an explicit filter such as --older-than or --source.
• --dry-run previews candidates without writing files.
• --lineage logical keeps compression chains together as one logical document.
• Each export writes/updates manifest.jsonl with path, message count, lineage ids, and SHA-256.
• --delete-after-verified is intentionally limited to one --session-id and requires --yes; it verifies the written file before deleting.

This keeps the dangerous operation narrow while making the safe archival path easy.

[teknium1]

Merged via PR #60186 (#60186) — thanks @web3blind!

Your commit was cherry-picked onto current main with your authorship preserved in git log. During salvage we restructured the surface per our conventions: instead of a separate export-md subcommand, your Markdown/QMD exporter now lives on the existing export subcommand as --format md|qmd, and we broadened it with the shared prune/archive filter set and an opt-in --redact pass. All your core work — the formatter, SHA-256 verification, compression-lineage export, manifest, and the guarded delete-after-verified flow — landed intact.