fix(cartridge): emit depends = base, contrib to match pilot convention (#25)

PR #24 emitted `depends = base` on the cartridge ipkg. The k9iser-mcp
pilot (and every other boj-server cartridge — 23 of them) ships
`depends = base, contrib`. Aligning to the established convention so
cartridge authors get `Data.List` / `Data.String` helpers etc. without
having to hand-edit the ipkg on day one.

The omission was based on a mis-diagnosis: PR #24's description claimed
`depends = base, contrib` was invalid in Idris2 0.8.0 because
`idris2 --check k9iser-mcp.ipkg` reported "Expected end of input" at
the comma. That subcommand is wrong for ipkg files — `--check` treats
files as Idris2 modules, not packages. `idris2 --build k9iser-mcp.ipkg`
(the correct invocation) succeeds with `1/1: Building K9iserMcp.SafeK9iser`
on Idris2 0.8.0. Re-verified locally against k9iser-mcp + the
chapeliser-mcp output of this scaffold (RC=0 on both).

Verification of this change:
- `iseriser cartridge` regenerates `chapeliser-mcp/abi/chapeliser-mcp.ipkg`
  with `depends = base, contrib`.
- `idris2 --build` on the regenerated ipkg: SafeChapeliser type-checks,
  RC=0.
- `cargo test`: 57 unit + 9 integration green.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: hyperpolymath

src/codegen/cartridge.rs

@@ -473,7 +473,7 @@ brief      = "{cartridge} cartridge — {lang} -iser regeneration"
 
 sourcedir  = "."
 modules    = {mcp}.Safe{module}
-depends    = base
+depends    = base, contrib
 "#,
         pkg = lower_pkg,
         cartridge = ctx.cartridge_name,