docs: add Mermaid diagrams, metrics page, and document new features
Replace all ASCII art diagrams with Mermaid.js across 7 pages.
Add Metrics & Observability page for pkg/metrics package.
Document intent classification, research phase, chunked planning,
coverage gates, and ship preflight in Six-Phase-Workflow.
Fix Edit tool risk level (medium → dangerous), update Grep with
ring buffer streaming and ReDoS protection, add O(1) dedup notes
to Code-Intelligence and Prompt-History pages.
docs: expand M31A to M31 Autonomous on first mention in all 21 wiki pages
Every wiki page that references the product now introduces the full name
"M31 Autonomous (M31A)" on first mention for brand recognition. Also
fixes install.sh URLs from /main/ to /master/ branch.
docs: add comprehensive 24-page wiki covering entire codebase
Covers architecture, six-phase workflow, tools system, provider system,
subagents, task runner, prompt system, code intelligence (4 language
parsers), token estimation, git integration, terminal UI (29 screens),
session management, prompt history, public packages, security model,
error handling, logging, file utilities, configuration reference,
slash commands, keybindings, and development guide.