docs: document all v1 route groups and endpoints in API.md

[olutundee]

Overview

Expands API.md to comprehensively document the entire API surface area across all ~24 mounted route groups in the Heliobond backend, providing an index matrix, authentication requirements, parameter tables, request/response JSON schemas, and error shapes.

Related Issue

Closes #476

Changes

Documentation & API Reference

• [MODIFY] API.md
  • Added top-level Discoverability Index Matrix mapping all ~24 mounted route groups, base paths, auth requirements, and rate limit tiers.
  • Added comprehensive documentation for previously missing route groups: Financial modeling, Forecasting, Project Comparisons & Rankings, Industry Benchmarking, Predictive Maintenance & Work Orders, Anomaly Detection, Webhooks, Email Digests, Multi-Chain broadcasting, Satellite data source failover, Custom Scoring Formulas & A/B testing, Role-Based Access Control (RBAC), and System Operations (DB migrations, secret rotation, dynamic log levels, compression stats, OpenTelemetry traces).
  • Documented query parameters, request body schemas, response payloads, error conditions, and authentication mechanisms for all endpoints.

Verification Results

$ npx prettier --check API.md
Checking formatting...
All matched files are using Prettier.

$ git diff --stat
API.md | 1204 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 984 insertions(+), 220 deletions(-)

Acceptance Criteria	Status
Top-level index/table of all mounted route groups	✅ Added comprehensive route group discovery matrix with auth and rate limiting tiers
Complete documentation for core & externally consumed endpoints	✅ Documented financial, forecast, comparison, benchmarking, maintenance, webhooks, and all other mounted groups
Accurate request/response schemas, parameters, and error shapes	✅ Verified against Express router definitions in src/routes/*.ts and src/index.ts
Markdown formatting	✅ Formatted and validated with Prettier

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