feat(parser): rework diagnostics and harden parser for v1

[zharinov]

Summary

• Refactor parser/: remove dead API surface, restore lossless-CST guarantees, drop allocations in hot paths, correct misleading lexer comments (verified against vendored logos/rowan/annotate-snippets sources)
• Rework parser diagnostics: consolidate naming-convention kinds, make fix patches verbatim-valid, polish all messages; cascade-suppressed rendering is now the user-facing default
• New diagnostics: unterminated strings, quantified/captured anchors (previously type-unsound — a captured anchor produced a phantom typed field), tree-sitter style dotted/hyphenated captures; enforce strict snake_case capture names; remove XML-garbage tokens

Why

Pre-v1 cleanup so upcoming syntax extensions land on a solid base. Strict snake_case captures chosen deliberately: capture names become Rust struct fields under the planned proc-macro compilation.

Notes

• CLI previously rendered unfiltered diagnostics — suppression only applied in tests; render/render_colored are now filtered, render_unfiltered kept for debugging
• Fix replacements previously didn't match their spans (e.g. (a) @Name suggested (a) name); all patches now substitute the annotated range verbatim
• Suppression rule added: a warning never outranks an error
• UnclosedString ranks above other unclosed kinds: a missing quote swallows closing delimiters, so it is the root cause