docs: complete feature coverage — aws tools, caching, dashboard, UI, CLI

[AhmadHammad21]

Summary

Fills the documentation gaps identified in the feature audit. Adds 5 new reference pages to docs/:

File	Covers
aws_tools.md	All 21 tools with params, return shapes, and usage tips (CloudWatch, CloudTrail, ECS, Lambda, EC2, RDS, IAM, bash tool, history tools)
caching.md	TTL cache mechanism, cache key design, interaction with tool capping
dashboard.md	Every dashboard panel explained — stat cards, activity chart, service breakdown, root causes, context management row
ui.md	Chat page, session sidebar, history page, settings page, dark mode
cli.md	All 5 commands (investigate, ask, report, ui, mcp) with flags and examples

Test plan

• All 11 docs files in docs/ render correctly as Markdown
• All tool names in aws_tools.md match the actual function names in src/tools/
• CLI flags in cli.md match actual Typer option definitions