Add docs/landscapes/vaultctl/ with design decision records

[f3rdy]

Description

Promote vaultctl to its own landscape with a structured place for design decisions. The tool has accumulated several cross-cutting design choices that should be discoverable outside of code comments and PR descriptions:

• Python over Go/Rust (sprachlicher Stack)
• CUE schema validation via subprocess (no native Python binding)
• Project-local `.vaultctl/` directory layout
• Schema inference via Python walker, not `cue import`
• Baseline + constraints split for hand-edited rules

Why a Landscape (and not just docs/decisions/)

Per the global Claude Code convention, landscapes are typically used to group cross-repo work for client engagements. Tool repos historically don't have landscapes. Deviation: vaultctl is now mature enough (v1.0.0) and has enough cross-cutting decisions to benefit from the same structure — LANDSCAPE.md + decisions/ + (eventual) patterns/ — even though it's a single-repo tool.

If the convention should win and we'd rather use `docs/decisions/` flat, easy to rename later.

Scope (this issue)

• Create `docs/landscapes/vaultctl/LANDSCAPE.md` — minimal entry point, lists current decisions.
• Create `docs/landscapes/vaultctl/decisions/` directory.
• First ADR: schema inference via Python walker vs `cue import` (the immediate motivation).
• Reference the landscape from project `CLAUDE.md` (per global pattern).

Subsequent ADRs (Python vs Go, CUE subprocess, .vaultctl/ layout) can be backfilled in follow-up PRs as they become relevant.

Files

• `docs/landscapes/vaultctl/LANDSCAPE.md` (new)
• `docs/landscapes/vaultctl/decisions/0001-schema-inference-via-python-walker.md` (new)
• `CLAUDE.md` (add landscape reference)

Priority

P3