vibeutils 0.9.2

Patch release. Fixes a memory safety bug in mktemp, consolidates
the symbolic mode parser, and adds POSIX umask support for
implicit-who symbolic mode clauses.

Bug Fixes

• mktemp: undefined memory beyond 256 X's. fillRandom used
  a fixed 256-byte getrandom buffer and silently left template
  positions past 256 as uninitialized stack memory. Templates like
  myapp.XXXX... (300+ X's) produced garbage bytes in the output
  filename. Now uses chunked getrandom calls to fill any length.
• mkdir: umask for implicit-who symbolic modes. mkdir -m =rw
  with umask 022 produced 666 (umask ignored). GNU applies umask
  to clauses without an explicit who-specifier (=rw, +x) per
  POSIX §4.7. Now produces 644, matching GNU.

Improvements

• chmod: deduplicate symbolic mode parser (-368 lines). chmod
  had its own 200-line symbolic mode parser duplicating the shared
  parser in common/mode.zig. Deleted the local copy; chmod now
  delegates to common.mode.parseSymbolic. Net removal: 609 lines
  deleted, 241 added.
• common/mode.zig: POSIX umask support. Activated the
  ModeContext.umask field (was reserved/unused). When no explicit
  who-specifier is given and the operator is + or =, the
  complement of the umask is applied per-class. - operations
  are never constrained. Both chmod and mkdir benefit.
• mktemp: document intentional GNU divergences. --tmpdir
  optional-value semantics (a getopt quirk no scripts rely on)
  and the now-fixed fillRandom limit are documented in the
  module doc comment.

Verified

• All unit tests pass on macOS and Linux.
• Full integration suite: 48/48 utilities on Linux.
• mkdir 112/112, chmod all passing on both platforms.
• Umask semantics match GNU: chmod +rw with umask 022 = 0644,
  mkdir -m =rw with umask 022 = 644, mkdir -m =rwx = 755.