Add AI-first Quickstart page; reconcile MCP tool count to 48

Broaden the audience by leading with the driving feature (AI) and giving
new users a single, short path to first value.

- New docs/quickstart.md: lean, AI-first onboarding (install -> drag in ->
  Enable Envoy -> talk to the live session), placed right after Home in the
  mkdocs nav. Every claim verified against EmbodyExt/EnvoyExt source: the
  "Enable Envoy?" prompt and Skip/Enable buttons, the git "Start Without Git"
  dialog, ~30 MB deps, localhost:9870, generated config files. Includes
  per-client "open the folder" steps, the account/sign-in prerequisite, and
  troubleshooting links so a non-coder doesn't get stuck before first payoff.
- docs/index.md: the Quick Start section now leads with a Quickstart button.
- web/index.html: prominent Quickstart CTA in the hero (new .btn--outline
  style in web/styles.css) plus a "Read the full Quickstart" CTA under the
  four-steps section; fixed a dead #getting-started footer anchor -> /quickstart/.
- web/README.md: corrected hero-CTA docs (three text CTAs plus a GitHub link).

Reconcile the Envoy MCP tool count to 48 across all current-facing surfaces
(previously drifted across 45/47). 48 matches the 48 @self.mcp.tool()
decorators in EnvoyExt.py and the 48 live server tools; the 4 bridge
meta-tools are counted separately. Updated docs/index, envoy/index
("15 categories, plus 4 bridge meta-tools"), tools-reference, launch-surfaces,
demo-storyboard, server.json, README, web/index, and web/envoy/index.
Historical changelog/release entries (46/42) left intact.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>