chore(claude): silence native install check for mise-managed install

[vaintrub]

Problem

~/.claude.json records installMethod: native, so Claude Code's startup/doctor check (rLq) probes ~/.local/bin/claude and warns on every launch. But claude is installed via mise/aqua (binary under ~/.local/share/mise/installs/..., on PATH via mise activation), so the native path is empty:

installMethod is native, but claude command not found at /home/vaintrub/.local/bin/claude

Fix

Instead of faking the native layout with a symlink, set two recognized env vars in .chezmoitemplates/claude-settings-base.json → ~/.claude/settings.json:

"env": {
  "DISABLE_INSTALLATION_CHECKS": "1",
  "DISABLE_AUTOUPDATER": "1"
}

• DISABLE_INSTALLATION_CHECKS=1 — verified against the binary: the check function early-returns (if (DISABLE_INSTALLATION_CHECKS) return []) before building any warning, so the native-mismatch warning and npm-deprecation / install-mismatch notices are suppressed. This is the intended escape hatch for externally-managed installs.
• DISABLE_AUTOUPDATER=1 — native self-updater stays off; mise/aqua owns versioning (mise upgrade aqua-anthropics-claude-code). autoUpdates:false was already set per-machine; this makes it portable.

Why not a symlink / not editing installMethod

• A ~/.local/bin/claude → mise-shim symlink works but is a fake-native-layout hack.
• Editing installMethod to a non-native value is worse: the binary's cleanup path Y08 runs when installMethod !== "native" and unlinks ~/.local/bin/claude — and ~/.claude.json is runtime-rewritten and not chezmoi-managed (non-portable).
• The env-var approach is portable via chezmoi, uses first-class recognized flags, and touches no filesystem outside settings.

Notes

• No change to what runs: claude still resolves via mise's activated install dir.
• DISABLE_INSTALLATION_CHECKS also silences npm-deprecation notices — desired for an externally-managed install.