Add README with protocol overview and project documentation

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+# Swiss Post E-Voting — Go PoC
+
+A ground-up reimplementation of the Swiss Post e-voting cryptographic protocol as a single Go binary.
+
+The Swiss Post system is Switzerland's official internet voting platform, used in binding federal elections. The production system spans **14 Java repositories, 500K+ lines of code, and requires 50GB of RAM**. This PoC distills the core cryptographic protocol into **52 Go files with 2 dependencies**.
+
+## What This Implements
+
+The full election lifecycle with end-to-end verifiability:
+
+```
+Setup        4 Control Components + Electoral Board generate keys
+             Voting cards with secret codes are produced
+                              |
+Vote         Voter encrypts ballot client-side (ElGamal)
+             Server validates zero-knowledge proofs
+             Return codes confirm vote was recorded correctly
+                              |
+Tally        5 sequential verifiable shuffles (Bayer-Groth)
+             Each shuffle: permute -> re-encrypt -> partial decrypt
+             Final decryption by air-gapped Electoral Board
+                              |
+Verify       Public audit: all proofs are independently checkable
+             No secrets required — anyone can verify the election
+```
+
+## Cryptographic Components
+
+| Package | What It Does |
+|---------|-------------|
+| `pkg/math` | Quadratic residue groups (G_q), safe prime generation, group vectors/matrices |
+| `pkg/elgamal` | ElGamal encryption, partial decryption, homomorphic ciphertext operations |
+| `pkg/zkp` | Schnorr proofs, exponentiation proofs, decryption proofs, plaintext equality proofs |
+| `pkg/mixnet` | Bayer-Groth verifiable shuffle with 6 sub-arguments (product, Hadamard, zero, SVP, multi-exponentiation, shuffle) |
+| `pkg/hash` | SHA-256 hash-and-square for Fiat-Shamir transforms |
+| `pkg/kdf` | HKDF key derivation for return code generation |
+| `pkg/symmetric` | AES-GCM authenticated encryption |
+| `pkg/returncodes` | Vote encoding as small primes, return code mapping tables |
+| `pkg/protocol` | Full election orchestration (setup, vote, confirm, tally) |
+| `pkg/verify` | Independent verification of all proofs |
+
+## Quick Start
+
+```bash
+go build -o evote ./cmd/evote
+
+# Run a complete election ceremony (10 voters, 3 candidates)
+./evote demo --voters 10 --options 3
+
+# Serve presentations on local network (for iPad viewing)
+./evote serve --port 8080
+
+# Theatrical step-by-step terminal walkthrough
+./evote present
+```
+
+## Demo Output
+
+```
+=== SWISS POST E-VOTING PROTOCOL PoC ===
+
+Phase 1: SETUP
+  Generated safe prime group (q: 256 bits, p: 257 bits)
+  CC[0]: generated ElGamal keypair, Schnorr proof OK
+  CC[1]: generated ElGamal keypair, Schnorr proof OK
+  CC[2]: generated ElGamal keypair, Schnorr proof OK
+  CC[3]: generated ElGamal keypair, Schnorr proof OK
+  EB: generated ElGamal keypair, Schnorr proof OK
+  Combined election public key (product of all 5)
+  Generated 10 voting cards with return codes
+
+Phase 2: VOTING
+  Voter 1: encrypted vote for option 2, proof verified
+  Voter 2: encrypted vote for option 0, proof verified
+  ...
+
+Phase 3: TALLY
+  Shuffle 1/5 (CC[0]): permute + re-encrypt + partial decrypt
+  Shuffle 2/5 (CC[1]): permute + re-encrypt + partial decrypt
+  ...
+  Final decryption by Electoral Board
+  Results: Option 0: 4 votes, Option 1: 3 votes, Option 2: 3 votes
+
+Phase 4: VERIFICATION
+  All 5 Schnorr key proofs: VALID
+  All 5 shuffle proofs: VALID
+  Vote count matches ballot box: VALID
+  Election integrity: VERIFIED
+```
+
+## Production vs. PoC
+
+| Aspect | Production (Swiss Post) | This PoC |
+|--------|------------------------|----------|
+| Group size | 3072-bit safe prime | 256-bit safe prime |
+| Codebase | 14 repos, 500K+ lines (Java) | 52 files, 15K lines (Go) |
+| Infrastructure | Kubernetes, HSMs, air-gapped machines | Single binary, your laptop |
+| Dependencies | Spring Boot, Bouncy Castle, Angular, ... | Cobra + stdlib crypto |
+| Memory | 50GB+ RAM | ~50MB |
+| Binary | N/A (Java services) | 9.5MB static binary |
+| Startup | Minutes (JVM + Spring) | Instant |
+
+## Presentations
+
+Three HTML slide decks are included, viewable in any browser or served to iPad via `./evote serve`:
+
+- **presentation.html** — Protocol overview: how a cryptographic election works
+- **presentation-crypto.html** — Deep dive into the mathematics (ElGamal, ZKPs, Bayer-Groth)
+- **presentation-swe.html** — Software engineering perspective: building a government election system in Go
+
+## Project Structure
+
+```
+cmd/evote/
+    main.go              Cobra CLI root
+    demo.go              Full election ceremony
+    serve.go             HTTP server for presentations
+    present.go           Theatrical terminal demo (772 lines)
+    web/                 Embedded HTML presentations
+pkg/
+    math/                Group theory (GQ, ZQ, vectors, matrices)
+    elgamal/             Encryption, decryption, key management
+    zkp/                 Zero-knowledge proofs (4 types)
+    mixnet/              Verifiable shuffle (Bayer-Groth, 12 files)
+    hash/                Hash-and-square, Fiat-Shamir
+    kdf/                 HKDF key derivation
+    symmetric/           AES-GCM
+    returncodes/         Vote encoding, return code mapping
+    protocol/            Election orchestration
+    verify/              Independent proof verification
+```
+
+## References
+
+- [Swiss Post E-Voting System Specification (PDF)](https://gitlab.com/swisspost-evoting)
+- Bayer, S. & Groth, J. (2012). *Efficient Zero-Knowledge Argument for Correctness of a Shuffle*
+- Haines, T. & Groth, J. (2020). *Verifiable Shuffle of Large Ciphertexts*
+- ElGamal, T. (1985). *A Public Key Cryptosystem and a Signature Scheme Based on Discrete Logarithms*
+
+## License
+
+MIT