Fix dashboard skills hub search reliability

[shannonsands]

Summary

• make dashboard Browse Hub searches timeout-safe with partial results instead of endless spinners
• keep known hub/source chips visible even when probing or featured loading fails
• add explicit frontend search/source error states and client-side abort timeout

Root Cause

• hub searches used Future.result(timeout=...) in a way that could miss concurrent.futures.TimeoutError, then block during executor shutdown when a source worker stalled
• source metadata probing could fail the whole dashboard source endpoint, hiding all hubs instead of surfacing degraded sources
• the frontend had loading state but no durable error/timeout state for Browse Hub searches

Validation

• source .venv/bin/activate && pytest tests/tools/test_skills_hub.py::TestParallelSearchSources tests/tools/test_skills_hub.py::TestUnifiedSearchDedup tests/hermes_cli/test_dashboard_admin_endpoints.py::TestSkillsHubSearchEndpoint tests/hermes_cli/test_dashboard_admin_endpoints.py::TestSkillsHubSourcesEndpoint -q
• npm --workspace web exec eslint -- src/pages/SkillsPage.tsx src/lib/api.ts
• npm run build --workspace web
• browser smoke on http://127.0.0.1:9123/skills: Browse Hub renders source chips and returns ethereum results with per-source counts

[teknium1]

Fixed in #43326 instead