bug(auth): preserve rc tokens before process.env can truncate embedded NULs

[betegon]

An access token containing an embedded NUL in .sentryclirc can be silently truncated before bearer validation sees it.

Confirmed locally against e0fdee49a347255bbbb072dfc74baf53ae5998de, using synthetic data and no network requests:

1. Parse INI content containing token = synthetic-prefix\u0000synthetic-tail with an actual NUL byte in the value.
2. parseIni preserves the complete string.
3. In CLI mode, getEnv() returns process.env.
4. applySentryCliRcEnvShim assigns the token to env.SENTRY_AUTH_TOKEN; Node truncates the value at the NUL.
5. The auth selector and bearer validator receive only synthetic-prefix, which is printable and passes format validation.

Expected: preserve the complete credential until it is validated, so an internal NUL is rejected without transmitting a truncated prefix. Surrounding padding may follow the shared token-normalization policy.

Do not simply throw from the boot-time shim: that runs before command routing and would also block help/login/logout, or reject an rc token that stored OAuth should ignore. Avoid switching identities by silently dropping the invalid token. A fix should preserve existing environment precedence and recovery commands, and account for context.env and subprocess inheritance if environment storage changes.

Suggested regressions: an embedded NUL in a selected rc token, an invalid rc token shadowed by stored OAuth, explicit env precedence, recovery commands, and parity between CLI/process.env and SDK/in-memory environments.

Relevant files: packages/cli/src/lib/ini.ts, packages/cli/src/lib/sentryclirc.ts, packages/cli/src/lib/env.ts, and packages/cli/src/cli.ts.