docs: comprehensive Rholang developer reference

[spreston8]

Summary

Adds a comprehensive, verified Rholang developer and AI agent reference under docs/rholang/. 19 topic files organized for both linear reading and targeted lookup. All content is verified against the Rust shard implementation (not inherited from RChain-era Scala docs).

Structure

Fundamentals

1. Language Overview -- process calculus, names vs processes
2. Syntax Reference -- complete syntax for all constructs
3. Data Types -- primitives, strings, byte arrays, URIs
4. Operators -- arithmetic, comparison, logical, string, interpolation

Types and Collections
5. Pattern Matching -- patterns, connectives, destructuring, type guards
6. Collections -- lists, tuples, sets, maps (all 50 methods verified)
7. PathMaps and Zippers -- hierarchical tries and cursor navigation
8. Numeric Types (file 15) -- Float, BigInt, BigRat, FixedPoint

Concurrency and State
9. Channels and Concurrency -- send/receive, persistent, peek, joins
10. Contracts and State -- cell pattern, CRUD, select, pitfalls

Platform
11. System Channels -- all 28 rho:* URIs with exact arities and calling conventions
12. Registry -- registry operations, TreeHashMap, standard library URIs
13. Vaults and Tokens -- SystemVault, MakeMint, auth keys, transfers
14. Cost Model -- phlogiston accounting with exact formulas from costs.rs

Patterns and Practice
15. Design Patterns -- capability security, ECDSA auth, nonce replay protection, method dispatch, persistent library reference, latest pointer, multi-level TreeHashMap
16. Rhox Macros -- .rhox template format
17. Testing with RhoSpec -- framework reference with real examples
18. Deployment Workflow -- CLI, HTTP, gRPC, WebSocket

Real-World
19. Real-World Applications -- Embers template-based contract generation, deploy flow, data model

Verification

Three verification passes against source code:

• System channels verified against rholang/src/rust/interpreter/system_processes.rs and rho_runtime.rs
• All 50 methods verified against reduce.rs method dispatch
• Cost model verified against rholang/src/rust/interpreter/accounting/costs.rs

Changes

• Renamed docs/rholang/README.md (crate overview) to crate-overview.md
• New docs/rholang/README.md is now the index
• Moved docs/rholang-language-analysis.md into docs/rholang/
• Preserved legacy RChain-era tutorials (rholangtut.md, rholangmatchingtut.md, ollama.md) with index entries noting they are legacy

Test plan

• All file links in README resolve
• All code examples are syntactically valid Rholang
• System channel URIs match system_processes.rs
• Method signatures match reduce.rs method_table
• Cost formulas match costs.rs