v0.1.17: UI fixes, Linux improvements, documentation overhaul

UI/UX:
- Fix heartbeat auto-refresh and rate-limiting page
- Add navigation breadcrumbs to settings pages
- New screenshots added

Linux Agent v0.1.17:
- Fix disk detection for multiple mount points
- Improve installer idempotency
- Prevent duplicate registrations

Documentation:
- README rewrite: 538→229 lines, homelab-focused
- Split docs: API.md, CONFIGURATION.md, DEVELOPMENT.md
- Add NOTICE for Apache 2.0 attribution

aggregator-server/internal/database/migrations/009_add_retry_tracking.up.sql

@@ -0,0 +1,9 @@
+-- Add retry tracking to agent_commands table
+-- This allows us to track command retry chains and display retry indicators in the UI
+
+-- Add retried_from_id column to link retries to their original commands
+ALTER TABLE agent_commands
+ADD COLUMN retried_from_id UUID REFERENCES agent_commands(id) ON DELETE SET NULL;
+
+-- Add index for efficient retry chain lookups
+CREATE INDEX idx_commands_retried_from ON agent_commands(retried_from_id) WHERE retried_from_id IS NOT NULL;