docs: CI workflow, architecture doc, README status update

[codeapplied]

Summary

• .github/workflows/tests.yml — runs the test suite on every push/PR to main, mirroring the sibling tender-tracking-system/data-enrichment-system repos' own CI. Real gap before this: only local pytest runs verified anything, nothing ran automatically on push.
• docs/ARCHITECTURE.md — data-flow Mermaid diagram, component breakdown, and the design decisions worth explaining (re-verification-via-merge-call, partial-failure handling, score-based primary selection, skip_pairs as data not code).
• README.md — status section updated (was still saying "discovery and merge execution are not built yet," which is now false), CLI section reflects --execute, added CI/license badges and a Development section.

Test plan

• 36 tests still passing after a fresh install
• tests.yml mirrors the sibling repos' already-working CI workflow shape exactly (same actions, same install command)