docs: organize documentation by feature

[rayyan224]

Summary

• Move all 17 current documentation files under docs/b20/.
• Add a feature-level docs/README.md index, leaving room for future sibling directories such as docs/feature-2/ and docs/feature-3/ without adding empty placeholders.
• Update incoming documentation links, source-code relative links, and the agent documentation map.
• Repair two existing stale links in the B20 overview.

Validation

• Verified all 17 original documents are preserved, except for the required link updates.
• Verified all 112 relative Markdown link targets across 20 files resolve.
• git diff --cached --check passed.
• Solidity tests were not run because this change only reorganizes documentation.

Generated with Toshi

[github-actions]

Interface Coverage

✅ All interface functions have test coverage.

[github-actions]

📊 Forge Coverage (src/lib/)

🟡 ≥95% across all metrics — some metrics below 99%.

File	Lines	Stmts	Branches	Funcs
🟡 B20FactoryLib.sol	97.70%	98.00%	100.00%	95.00%
🔴 test/lib/ForceFeeder.sol	0.00%	0.00%	100.00%	0.00%
🔴 test/lib/PrecompileProbe.sol	0.00%	0.00%	0.00%	0.00%
🟢 MockActivationRegistry.sol	100.00%	100.00%	100.00%	100.00%
🟢 MockActivationRegistryStorage.sol	100.00%	100.00%	100.00%	100.00%
🟢 MockB20.sol	100.00%	99.68%	100.00%	100.00%
🟢 MockB20Asset.sol	100.00%	100.00%	100.00%	100.00%
🟡 MockB20Factory.sol	98.96%	99.10%	100.00%	100.00%
🟢 MockB20Stablecoin.sol	100.00%	100.00%	100.00%	100.00%
🟢 MockB20Storage.sol	100.00%	100.00%	100.00%	100.00%
🟢 MockBaseTime.sol	100.00%	100.00%	100.00%	100.00%
🟡 MockPolicyRegistry.sol	100.00%	99.58%	97.78%	100.00%
🟢 MockPolicyRegistryStorage.sol	100.00%	100.00%	100.00%	100.00%
Total	97.14%	97.51%	98.21%	97.07%

Full report: download artifact. To browse locally: make coverage (runs forge coverage + genhtml + opens the HTML report).

[github-actions]

✅ Fork tests: 794 passed, 0 failed, 14 skipped

The completed Denim suite passed. Skipped tests were not validated.