fix(angular): use fail-fast error handling for invariant violations and remove panics

[Brooooooklyn]

• Make i18n metadata type checks fail-fast (return early) instead of
  silently dropping placeholders, matching Angular's throw behavior
• Make unknown @for loop variable checks fail-fast instead of emitting
  empty expressions, matching Angular's AssertionError throw
• Add 4 unit tests for the fail-fast behavior
• Replace all panic!/unreachable!/debug_assert! in production code with
  diagnostics-style error reporting or safe fallbacks (10 instances)

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

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Note

Medium Risk
Touches core compiler ingestion/optimization paths and changes error-handling semantics to early-return with diagnostics, which can alter emitted IR/output on previously tolerated invalid states.

Overview
Aligns Angular template ingestion with Angular’s fail-fast behavior by treating unexpected i18n metadata and unknown @for loop variables as hard errors: convert_i18n_meta_to_placeholder/get_computed_for_loop_variable_expression now return Result, callers early-return to avoid emitting broken IR, and new unit tests cover these cases.

Across several pipeline/output phases, replaces panic!/unreachable!/debug_assert!-guarded invariants with diagnostics plus safe fallbacks (e.g., cloning WrappedIrNode → undefined, skipping multi-line arrow function conversion, handling short safe-ternary chains, reporting unexpected UpdateOp variants, and graceful CSS quote handling).

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[Brooooooklyn]

• fix(angular): use fail-fast error handling for invariant violations and remove panics #37 👈 (View in Graphite)
• main

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