[docs] CONTRIBUTING.md: dev setup + branch naming + PR process + quality gates

[ozpool]

Context

Contribution guide. Establishes conventional commits, quality gates, PR expectations.

Scope

In scope:

• Dev setup steps
• Branch naming
• PR process + review expectations
• Quality gates (forge test, slither, aderyn, typecheck, lint)

Out of scope:

• Anything not listed above.

Acceptance Criteria

• File committed and linked from README where relevant
• No broken internal links
• Matches current architecture (verified against code)

Dependencies

• Blocks: —
• Blocked by: —

References

• N/A

Estimate

S

[ozpool]

PR opened — codifies dev setup, branch naming, conventional commits (no AI attribution), per-layer quality gates, ADR procedure.