Adopt shared-SA model, add DEPLOY guide, MIT license

- Install flow now assumes one admin-distributed service account JSON shared
  across the team. Each user creates their own Google Sheet and shares it
  with the SA email; per-user GCP project setup is gone.
- DEPLOY.md: a step-by-step walkthrough for non-technical users following
  along with an AI agent (Terminal basics, screenshots-worth of expected
  output, common-error table).
- scripts/append_row.py: sheet_id field accepts either a bare ID or a full
  Google Sheets URL; normalize_sheet_id() extracts the ID via regex.
- scripts/setup.md: rewritten as an admin guide (one-time GCP setup, key
  rotation) plus a troubleshooting reference.
- LICENSE: MIT (previously "private — internal use"). README license
  sections updated to match.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Knowit
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
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+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
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+
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