#794)

## Summary

Addresses the `LD_PRELOAD` RCE vector demonstrated in
[getsentry/action-release#315](getsentry/action-release#315).
A contributor PR to any Craft-using repo could plant a `.craft.env` file
containing `LD_PRELOAD=./preload.so` plus a malicious shared library;
when Craft ran in CI it would hydrate `process.env.LD_PRELOAD` and every
subprocess Craft spawned (git, npm, gpg, docker, etc.) would load the
attacker's code with access to all release secrets.

This PR removes the primary vector and hardens three adjacent surfaces
so a future regression (or an earlier CI step planting dangerous env
vars) cannot be similarly weaponised.

## Changes

### 1. Remove `.craft.env` file reading (primary fix)
- `src/utils/env.ts`: delete `readEnvironmentConfig`, `ENV_FILE_NAME`,
`checkFileIsPrivate`. Add `warnIfCraftEnvFileExists()` which only calls
`existsSync` and emits a one-time warning per legacy file location,
pointing users at the shell / CI environment. **`process.env` is never
hydrated from a file again.**
- `src/index.ts`: swap the call site.
- `package.json` / `src/types/nvar.ts`: drop the `nvar` dependency and
its type shim.
- `docs/.../getting-started.md`: replace the "Environment Files" section
with a short note that credentials must come from the shell / CI.

### 2. Strip dynamic-linker env vars at startup (defence-in-depth)
- `src/utils/env.ts`: new `sanitizeDynamicLinkerEnv()` deletes
`LD_PRELOAD`, `LD_LIBRARY_PATH`, `LD_AUDIT`, `DYLD_INSERT_LIBRARIES`,
`DYLD_LIBRARY_PATH`, `DYLD_FRAMEWORK_PATH`,
`DYLD_FALLBACK_LIBRARY_PATH`, `DYLD_FALLBACK_FRAMEWORK_PATH` from
`process.env` with a per-key warning. Values are never logged.
- Emergency escape hatch: `CRAFT_ALLOW_DYNAMIC_LINKER_ENV=1` preserves
the vars but emits a noisy info-level log naming which keys were
preserved.
- Called from `src/index.ts` as the very first thing `main()` does.

### 3. Allowlist env forwarded to `preReleaseCommand` (breaking change)
Previously `runCustomPreReleaseCommand` in `src/commands/prepare.ts`
forwarded `{ ...process.env, ...additionalEnv }` to the subprocess —
anything in the parent env (including `LD_PRELOAD`, cloud credentials,
etc.) leaked through.

- New `src/utils/releaseCommandEnv.ts` exports `ALLOWED_ENV_VARS` and
`buildReleaseCommandEnv(extras)` which returns `{ PATH, GITHUB_TOKEN,
HOME, USER, GIT_COMMITTER_NAME, GIT_AUTHOR_NAME, EMAIL, ...extras }`.
- `prepare.ts` and `publish.ts` both use the shared helper.
`runPostReleaseCommand` behaviour is unchanged — it already used an
inline allowlist — but the inline code is replaced with the shared
helper.
- **Breaking**: pre-release scripts no longer inherit arbitrary env
vars. If a script needs additional variables, rename them with a
`CRAFT_` prefix (yargs auto-promotes `CRAFT_*` to CLI options) or have
the script source them from a secrets file.

### 4. Gate `--config-from` behind `--allow-remote-config` (breaking
change)
`--config-from <branch>` fetches `.craft.yml` from a remote git ref via
`git show` and feeds it to `loadConfigurationFromString`, which
configures the `preReleaseCommand` that Craft later executes. That's
effectively arbitrary-command execution from a network-fetched payload.

- `src/commands/prepare.ts`: new `--allow-remote-config` flag (also
honoured as `CRAFT_ALLOW_REMOTE_CONFIG=1`).
- Exported `assertRemoteConfigAllowed()` helper throws
`ConfigurationError` naming the branch and the opt-in flag when
`--config-from` is used without the opt-in. When opted in, Craft logs a
warning identifying the branch.

## Testing

- **New tests** (`src/utils/__tests__/env.test.ts`): 5 tests for
`sanitizeDynamicLinkerEnv` covering all keys, opt-out behaviour,
value-not-in-log property; 5 tests for `warnIfCraftEnvFileExists`.
- **New tests** (`src/commands/__tests__/prepare.test.ts`): planted
`LD_PRELOAD` / `AWS_SECRET_ACCESS_KEY` / `SECRET_TOKEN` in `process.env`
and assert none reach the spawn env; 3 tests for
`assertRemoteConfigAllowed`.
- **New test** (`src/commands/__tests__/publish.test.ts`): same
attacker-planted-env regression for `runPostReleaseCommand` (locks in
the existing allowlist behaviour).
- Full suite: 947 passed (same 7 pre-existing environmental failures in
`prepare-dry-run.e2e.test.ts` as on master; unrelated).
- `pnpm build` passes; `pnpm lint src/` reports 0 errors (only
pre-existing warnings).

## Verification steps

1. `pnpm install && pnpm test && pnpm build` — all pass.
2. `rg -n "nvar|ENV_FILE_NAME|readEnvironmentConfig" src/ docs/src/` —
no hits.
3. Plant `.craft.env` next to `.craft.yml` in a scratch dir; Craft warns
and does **not** load it.
4. Export `LD_PRELOAD=x` in your shell and run `./dist/craft --help` —
Craft strips it and warns.
5. `./dist/craft prepare --config-from some-branch 1.0.0` — rejected
with a `ConfigurationError` naming `--allow-remote-config`.

## Breaking changes

See the commit body. Summarised:
- `.craft.env` is no longer read; use shell / CI env instead.
- `preReleaseCommand` receives only allowlisted env vars.
- `LD_PRELOAD` / `DYLD_*` are stripped at startup (override:
`CRAFT_ALLOW_DYNAMIC_LINKER_ENV=1`).
- `--config-from` requires `--allow-remote-config` (override:
`CRAFT_ALLOW_REMOTE_CONFIG=1`).