Add runtime egress enforcement and audit logging

[initializ-mk]

Summary

• Runtime egress enforcement via EgressEnforcer — an http.RoundTripper that validates every outbound HTTP request against the resolved domain allowlist before forwarding. Supports exact match, wildcard domains (*.github.com), and always-allowed localhost. Three modes: deny-all, allowlist, dev-open.
• Structured audit logging with NDJSON events (session_start, session_end, tool_exec, egress_allowed, egress_blocked, llm_call) and correlation IDs for end-to-end request tracing.
• Context-threaded correlation — TaskID and CorrelationID propagated through context and HookContext, attached to all audit events including egress callbacks.
• Tool wiring — all HTTP-making tools (http_request, mcp_call, webhook_call, web_search_tavily, web_search_perplexity) now use the egress-enforced transport/client from context.
• Comprehensive README rewrite covering fallback chains, OAuth, memory, runtime security, guardrails, context budgeting, config reference, and environment variables.

Files changed

File	Change
forge-core/security/egress_enforcer.go	NEW — http.RoundTripper wrapper + context helpers
forge-core/security/egress_enforcer_test.go	NEW — unit tests
forge-core/security/egress_integration_test.go	NEW — end-to-end tests with httptest
forge-core/runtime/audit.go	NEW — NDJSON audit logger + context helpers
forge-core/runtime/audit_test.go	NEW — unit tests
forge-core/runtime/audit_integration_test.go	NEW — event sequence tests
forge-core/runtime/hooks.go	MODIFY — add TaskID/CorrelationID to HookContext
forge-core/runtime/loop.go	MODIFY — populate IDs in all 5 Fire() calls
forge-core/tools/builtins/http_request.go	MODIFY — use egress transport
forge-core/tools/builtins/web_search_tavily.go	MODIFY — use egress client
forge-core/tools/builtins/web_search_perplexity.go	MODIFY — use egress client
forge-core/tools/adapters/mcp_call.go	MODIFY — use egress transport
forge-core/tools/adapters/webhook_call.go	MODIFY — use egress transport
forge-cli/runtime/runner.go	MODIFY — resolve egress, build enforcer, inject context, register audit hooks
README.md	REWRITE — comprehensive documentation

Test plan

• forge-core/security — all egress enforcer tests pass (allowlist, deny-all, dev-open, wildcards, localhost, callbacks, context helpers, integration)
• forge-core/runtime — all audit logger tests pass (emit, concurrent safety, context round-trips, event sequence)
• forge-core/tools — existing tool tests pass unchanged (backward compatible when no egress client in context)
• forge-cli/runtime — runner tests pass with updated registerHandlers signature
• golangci-lint clean on both forge-core and forge-cli