Refactor/better error handling

[devoreofox]

Better error surfacing: non-throwing parser + unified diagnostics

Reworks how the plugin reports authoring errors, on two fronts: stop using exceptions for expected parse failures, and surface every problem consistently in one place.

Parser: exceptions to results

• Tokenizer and Parser no longer throw. They report failures through a Condition.TryParse(expression, out node, out error) facade instead.
• ConditionException is deleted, along with its four catch sites.
• This matters most in the editor: the highlighter re-parses visible conditional lines every frame, so a half-typed :if used to throw and catch an exception ~60 times a second. That cost is now gone.

Structured diagnostics

• New Diagnostic record (message, optional line number, severity) plus a Severity enum (Error, Warning).
• The four validators (blocks, sets, waits, untils) now return IEnumerable<Diagnostic> instead of a single string?, so they report every problem rather than just the first.
• New AliasValidator.Validate aggregator runs all validators and folds cycle detection into the same list.

One consistent surface

• The alias editor now lists all current problems together, each with its line number and a color for its severity (red for errors, amber for warnings).
• Cycle detection moved out of the trigger field's hover tooltip and into that panel, so a recursive alias is no longer hidden behind a mouseover. The tooltip is back to being pure help text.
• Added a configurable Warning theme color (auto-picks up a settings swatch via the existing reflection). Today the only warning is a :until -unsafe used while unsafe waits are disabled.

Tests

• ConditionEvaluatorTests: malformed expressions now assert a false result instead of a thrown exception.
• AliasValidatorTests: updated to the new return type, plus coverage for per-line reporting and multiple diagnostics from one alias.