docs(readme): add isfr, agent-reputation, marketplace to module map

[JaeLeex]

Adds the three modules from the 2026-05-28 Jacob ↔ Nunchi sync to the README module map. Oracle was already listed, so this only adds ISFR, Agent Reputation, and Marketplace.

Placement

• New ### Agents category (between Network Infrastructure and Finance) for Agent Reputation and Marketplace — placed above Finance so dependency arrows keep pointing "up."
• ISFR added under Finance, next to Derivatives (it's the first concrete interest-rate-index instance), depending on oracle, coins, agent reputation, and marketplace.
• Identity kept as a minimal key pair per Jacob ("the identity is a key pair") — no heavy registry.

Tracking issues

• module: oracle — off-chain data ingestion + time-series DB #3 module: oracle (already in the map)
• module: isfr — agent-computed interest-rate index (depends on oracle) #4 module: isfr
• module: agent-reputation — epoch-rotated, reputation-gated agent selection #5 module: agent-reputation
• module: marketplace — job posting, discovery, settlement #6 module: marketplace

Note

ISFR's on-chain vs. DB-first question is intentionally left open (see #4) for the Portugal in-person — this PR only registers the module in the map, it doesn't commit to an implementation path. Reputation should reconcile with the existing daeji/crates/agents/agent-qualification crate.

Docs-only change; no code touched.