docs: rewrite README as a positioning-first pitch

[kosminus]

What

Rewrites the README as a positioning-first pitch (~200 lines, down from ~850) and relocates the deep documentation it displaced into docs/ — nothing is deleted, only moved.

Why

The old README was excellent documentation but a weak landing page: it opened with an implementation description instead of a value proposition, buried the differentiators (governance, self-hosted/BYO-LLM, MCP) in a 22-bullet feature wall, used none of the 9 screenshots in screenshots/, had a literal <repo-url> placeholder in the Quick Start, and overclaimed the model routing ("haiku → sonnet → opus") versus what the router actually does.

Changes

• README.md — restructured top-to-bottom:
  • Tagline ("Governed, self-hosted text-to-SQL…") + three-sentence positioning naming the audience, problem, and wedge
  • Badges (CI, MIT, Python 3.12, React 19, connectors) and a hero screenshot (screenshots/query2.png) alongside the demo video
  • Four "Why QueryWise" differentiators replace the flat 22-bullet list; the full feature set survives as a grouped, compact section
  • Quick Start fixed with the real clone URL and an explicit "try everything before connecting your own DB" hook
  • Pipeline diagram corrected: routing now described as complexity classification + token budget (matches app/llm/router.py); roles corrected to viewer/editor/admin
  • Compact sections retained for MCP (teaser + 2 commands), production deployment, security, and the IFRS 9 sample; new Documentation index table
• docs/mcp.md (new) — full MCP guide: all five client configs (Claude Code/Desktop, Cursor/Windsurf, Copilot, Codex), transports, and the network-reachability matrix
• docs/configuration.md (new) — env-var table, LLM provider selection + Ollama setup + provider-switching notes, and the host-DB / BigQuery / Databricks connection guides
• docs/api-reference.md (new) — the REST endpoint tables (plus health probes)
• docs/development.md (new) — no-Docker setup, test/lint commands, the full project-structure tree, and the connector/LLM-provider extension guides

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