refactor(validation): tokenize shell-safe command pattern

Replace the flat character-class regex for SHELL_SAFE_COMMAND_PATTERN with
a token-aware alternation. The parser now recognizes explicit tokens
(`&&`, `||`, balanced single/double quotes, whitespace, and an unquoted
safe-char run) instead of a bag of characters, which lets us extend the
accepted grammar without loosening the guarantees.

New surface area, with tests:
- logical OR chaining (`make build || make clean`)
- shell globs and bang (`rm *.tmp`, `cp src/?.js dist/`, `! grep -q foo`)
- single-quoted arguments are now treated as balanced runs rather than
  rejected per-character

Preserved surface area:
- && chaining, balanced "..." and '...' quotes, the previous safe path /
  argument characters, and the existing error-path contract in
  ApplicationDeploymentJob::validateShellSafeCommand().

Also refreshes the user-facing validation messages in General.php so the
allow/deny list shown on failure matches the new grammar.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>