v0.2.2

Implements Synod 0.2. Errors now look like a good compiler's: on a terminal,
every compile-time and run-time error shows the source line, underlines the
exact problem, points at related places ("first defined here", "called from
node context here", "this is 0") and shows the fix as a diff. Piped output,
which agents and CI read, is unchanged byte for byte.

Added

• --style rich|short and --color auto|always|never on synod fmt, check and run (both --flag value and --flag=value; a bad value exits 2). Rich output draws the source line with markers, labels, notes and help under the unchanged first line; it is the default when the destination is a terminal. Piped or redirected output stays the one-line form byte for byte. Color needs NO_COLOR unset or empty and TERM other than dumb; the flags beat the environment. --json ignores both flags.
• synod run failures render a snippet under the failed at … line in rich style.
• check.json diagnostics gain end, and label, labels, help (with edits) and notes when present; the format stays synod-check/1.
• A diagnostic without a position prints as path: error[code]: message.
• Fixes shown under help: for missing parentheses, imports to add, remove
  or rename, the package header, canonical form, receivers, sim.Nobody,
  "did you mean" names and more; each is tested to remove its error.
• Hidden control and bidi characters in source are neutralised in snippets,
  so a file cannot inject terminal escapes.
• Golden cases of testdata/check have expect-rich.txt and expect.json next to expect.txt; testdata/run/errors cases have expect-rich.txt.