docs: README cleanup — markets, quick start, strategy tiers

[JaeLeex]

Summary

• Restructure Quick Start around testnet-as-default and the --mainnet + HL_TESTNET=false requirement.
• Add a dedicated Markets & Instruments section separating native HL perps, Paragon osrs/para BTCSWP swap perps, and YEX yield markets (no more conflating YEX with Paragon mainnet BTCSWP).
• Add honest strategy tiers (quoting_engine vs standalone vs experimental) and fix stale counts (19 strategies, 1300+ tests, 20 MCP tools).
• Align top Railway deploy button with the hosted MCP runtime docs (was still pointing at legacy APEX template).

Stacks on #63 (jl/osrs-para-btcswp-mainnet-markets).

What was wrong in the old README

• Markets buried at the bottom under a single “YEX & BTCSWP (mainnet)” heading that mixed YEX testnet yield perps with Paragon mainnet swap perps.
• No mention of BTCSWP-OSRS / osrs:BTCSWP testnet Paragon swap perp.
• Quick start implied engine_mm as the default first run; didn’t explain env/flag consistency checks.
• Stale badges (14 strategies, 483 tests, 16 MCP tools) and contradictory Railway button (APEX template vs MCP runtime section).
• grid_mm incorrectly marked as requiring quoting_engine.

Test plan

• Markdown renders; anchor links resolve
• Reviewers confirm instrument names match cli/strategy_registry.py on feat: osrs/para BTCSWP swap perps + mainnet HIP-3 dex support #63 branch

Made with Cursor

[JaeLeex]

Merge order (stacked chain): #63 → #64 → #65 → #66

Rebased #65 onto this branch (jl/readme-cleanup); #66 stacks docs/deploy cleanup on #65.