webapi: derive SVG prototype chains

[mh0pe]

Summary

• replace three fixed-depth SVG factory helpers with one compile-time _proto walker
• preserve SVG tag casing and namespace while initializing arbitrary graphics and geometry chains
• add hierarchy coverage for parser-created nodes and createElementNS

This reauthors the factory-chain subset of #2157 on top of the SVG hierarchy merged in #2917 instead of replaying the obsolete implementation.

Atomic stack

1. webapi: derive SVG prototype chains #3012 — prototype-chain foundation
2. webapi: add live SVG scalar values #3034 — live scalar values
3. webapi: add live SVG collections #3030 — live collections
4. webapi: implement SVG geometry #3033 — geometry and paths
5. webapi: add SVG structural elements #3031 — structural elements
6. webapi: add live SVG resource elements #3029 — resource elements
7. webapi: add dependency-free SVG text DOM #3032 — dependency-free text DOM

Dependent units are ready for review and remain stacked on their preceding branch history so every owning commit stays explicit.

Validation

• rebased onto current main at 6f82bdcd
• zig fmt passed
• full release suite passed: 1,090 of 1,090 tests
• full debug/TSAN suite passed: 1,090 of 1,090 tests
• final-stack CI evidence: https://github.com/mh0pe/browser/actions/runs/29922276068

The workflow aggregate is red only because the fork cannot pull the private ghcr.io/lightpanda-io/perf-fmt container; that job executed no repository code.

[mh0pe]

@pinetops @staylor could I get a review please?

[karlseguin]

@pinetops @staylor could I get a review please?

Looks fine to me. I didn't look at the other SVG changes planned, but I understand why this is helpful. You might want to rebase those before opening since the Zig 0.16 merge requires it (I've rebased this one).

Just waiting for the CI to finish, but I need to step out for ~1 hour.