Prepare spec repo for v1.0 launch

[damonfmcmillan]

Summary

• Remove stale demo/ directory (TPC-DS data, missing GDLA layer)
• Update specs: remove premature benchmark claims from GDLS, fix dead "greppable tooling repo" links in GDLA and GDLM
• Update README, logo, and prompts for v1.0 (lean, no unverified claims)
• Add gdl-lint.sh format linter covering all 7 GDL layers with 73 conformance tests
• Add CI workflow, contributing guide, changelog, and grep pattern reference docs

Key decisions

• grep -oP patterns preserved in GDL-SPEC.md and GDLM-SPEC.md (tracked in greppable/greppable#74)
• Benchmark claims removed from GDLS-SPEC.md pending results at greppable/benchmarking
• CI lint job gracefully skips when no GDL files exist outside tests/fixtures/

Test plan

• bash tests/test-gdl-lint.sh — 73/73 pass
• No plugin references in scripts/tests
• Original grep -oP patterns preserved
• Specs not in scope (GDL, GDLC, GDLD, GDLU) unchanged
• Code review issues addressed (CI skip, benchmark URL, pattern consistency, changelog accuracy)

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