feat: card standalone — primitiva de identidad soberana (hoja, autocontenida)

Tarjeta de Presentación canónica: identidad arje + flujos tipados brahman,
content-addressed. Hoja pura sin deps internas — la base sobre la que se
montan red (chasqui/minga) y escritorio. cargo check pasa (3 crates).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

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+# card
+
+> The canonical **presentation card** — sovereign identity + typed flows, in Rust.
+
+`card` is the suite's identity primitive: a content-addressed *Tarjeta de Presentación* that binds an `arje` identity to typed `brahman` flows. It is the leaf that the networking and desktop layers build on — peers, channels and capabilities are all expressed in terms of cards.
+
+## Crates
+
+- **`card-core`** — the canonical card type (identity + typed flows), content-addressed.
+- **`card-wit`** — WIT-typed flow descriptions (component-model interfaces).
+
+## How dependencies work
+
+A true leaf: `card` has **no internal dependencies** — only crates.io. It compiles standalone and is git-depended by the rest of the suite (networking via `chasqui`/`minga`, the desktop, etc.).
+
+## License
+
+MIT.