docs: full mdBook site + GitHub Pages deploy; rewrite README as project front page

- docs/: an mdBook documentation site — thesis, architecture, measurement
  discipline, equivalence gates, agent loop, isolation/anti-reward-hacking,
  playbook, ROI, reproduce, roadmap, and the five case studies (pulled from
  their single source in results/ via {{#include}}). Builds clean (21
  pages).
- .github/workflows/docs.yml: builds mdBook and deploys to GitHub Pages on
  push to main (one-time setup: Settings → Pages → Source = GitHub Actions).
- README.md: rewritten as the project front page — the thesis, the verified
  results table, layout, quick start, how it stays honest, links to the
  book. Replaces the stale Phase-0-era text.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

docs/src/introduction.md

@@ -0,0 +1,46 @@
+# hotpath
+
+> Spot cooling for hot paths. A profile-guided optimization agent that
+> only ships wins it can prove.
+
+hotpath profiles real binaries and services, isolates hot paths, proposes
+optimizations, and accepts a change **only** when two independent bars are
+cleared:
+
+1. **Behavioral equivalence** — the change provably preserves behavior
+   (upstream tests, byte-identical golden replay, differential fuzzing,
+   sanitizers) or it is discarded.
+2. **Statistical significance** — the speedup's bootstrap 95% CI lower
+   bound clears a threshold on trusted, calibrated hardware.
+
+Everything else is commentary. A change without both is not a win; it is a
+ledger row explaining why not.
+
+## What it has actually done
+
+Every number here carries its 95% confidence interval and its workload,
+and every one survived the gates above. These are not projections.
+
+| Result | Verified |
+|---|---|
+| tokei (Rust) — three compounding class-5 algorithmic wins | +10.7%, +3.7%, +9.9%, each CI-significant |
+| tokei — link-time optimization (class 1) | +10.4%, CI [+8.5%, +12.0%] |
+| cJSON (C) — number-handling rewrite (class 5) | +8.85%, CI [+7.5%, +10.0%] |
+| cJSON HTTP service — p50 latency under replayed load | +6.2%, CI [+5.8%, +7.2%] |
+| comrak (Rust) — mimalloc allocator swap (class 2) | +4.6%, CI [+3.3%, +5.8%], human-ruled |
+
+Across **five phases and 33 ledger rows**, with **zero shipped false
+accepts** — including two occasions where the pipeline itself over-accepted
+and the audit caught it before anything shipped, each becoming a permanent
+new gate.
+
+## The differentiator
+
+Consultants sell surveys; compilers sell flags. hotpath sells **verified
+deltas with the methodology attached** — a stopwatch on pinned hardware,
+a proof of equivalence, and an ROI figure whose confidence interval you
+can quote to a hostile reviewer. That is the entire product, and this site
+is how it works.
+
+Start with [the thesis](./thesis.md), or jump to a
+[case study](./case-studies/overview.md).