Add CLAUDE.md and a prominent vibe-coded disclosure in the README

pansy is written by an LLM with a human directing. That belongs near the top of
the README, not in a footnote — someone deciding whether to self-host this and
point it at their own data should know before they decide, not after. The
disclosure says what it actually means in practice (less scrutiny than a
hand-written project, read the code, back up the database) rather than a vague
"AI-assisted" hedge.

CLAUDE.md collects the operational details that otherwise get rediscovered every
session: GOWORK=off, the store/service/api seam and why rules go in the middle
layer, the two unit scales, version-guarded writes, ErrNotFound-as-existence-mask,
the branch/Gadfly/merge/deploy loop, and the env var names that aren't guessable.
It also makes the disclosure a standing rule: if the README is ever rewritten,
that section survives the rewrite, and the only acceptable edit is a clearer one.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

README.md

@@ -2,6 +2,12 @@
 
 Self-hostable garden planner: drag beds, bags, and containers onto a real-scale field, click into them to place freeform plops of plants, and zoom out to see what's planted where. Go backend + React frontend, one static binary.
 
+> ### 🤖 This is a vibe-coded project
+>
+> **Essentially all of the code in pansy was written by an LLM** (Claude), with a human directing the work, reviewing it, and deciding what ships. Every pull request also gets an automated adversarial review before it lands.
+>
+> That's said up front because you deserve to know it before you trust pansy with anything: it hasn't been through the kind of scrutiny a hand-written, widely-used project has. Read the code before you self-host it. Back up your database. Bugs here are the ordinary kind of bugs, not a scandal — but so is the fact that nobody hand-wrote the thing.
+
 See [DESIGN.md](DESIGN.md) for the architecture. Work is tracked in this repo's issues — start from the tracking epic.
 
 ## Quickstart