fix(desktop): trim session-list payloads

[sitkarev]

Summary

• trim heavy internal system_prompt / model_config fields from /api/sessions and /api/profiles/sessions list payloads
• keep detailed session APIs unchanged; the Desktop sidebar only needs list metadata
• add regression coverage so large cached prompts are not serialized in session-list responses

Why

On a real Desktop profile with many long-running/compressed sessions, each sidebar refresh returned full cached prompts for ~50 rows. That made responses multi-megabyte, pegged the single hermes serve backend at ~100% CPU, and caused /api/status / navigation to time out.

Observed locally before the fix:

• Desktop backend wedged at ~100% CPU / ~1.4GB RSS
• /api/status timed out
• session-list payload was ~2.2MB for 50 rows, mostly cached prompts

After the fix on the same profile:

• /api/status: 200 in ~0.09s
• authenticated /api/sessions?limit=50&offset=0&min_messages=1&archived=exclude&order=recent: ~64KB in ~0.26s
• no system_prompt / model_config fields in list rows

Tests

• uv run python -m pytest tests/hermes_cli/test_web_server.py -k 'sessions and (heavy_internal_prompt_fields or tags_default_profile or forwards_min_messages or order_recent)' -q
• uv run python -m py_compile hermes_cli/web_server.py tests/hermes_cli/test_web_server.py

[kshitijk4poor]

Closing in favor of #60883 (merged) — it covers this PR's field-trim (via #43653's strip + #47437's SQL-level compact_rows projection, so the blob is never even read off disk) plus messages pagination. Your diagnosis of the multi-megabyte sidebar refreshes is credited. Verified against main @ 31e39de.