Linux: modernize Ubuntu 26 build and ImageLoader

[jzhvymetal]

Summary

• add a reproducible Ubuntu 26 development/build path
• build ImageLoader against maintained system PNG, GIF, JPEG, and TIFF libraries
• add generated image fixtures, JNI/ELF validation, malformed-input containment checks, packaging, and server smoke tests
• package the Ubuntu media utilities needed by the supported runtime

Validation

• Java and native builds passed in the Ubuntu 26 Vibe build environment.
• JNI exports, ELF dependencies, ImageLoader fixtures, packaging, and server smoke gates passed.

Dependency

This is an intentional four-commit stack beginning with the GCC 15/64-bit compatibility topic.

Review state

Draft while the Ubuntu/native-library stack is split into independently reviewable maintenance changes. The applicable changes are intended for canonical SageTV so it can build and run on a current Ubuntu base with current GPU driver/userspace packages; upstream still needs to agree on the supported Linux, Windows, and macOS native-library matrix before merge.

---

This replaces OpenSageTV#14, which was opened against an intermediate fork instead of the canonical SageTV repository. The topic was replayed onto current canonical master; its only conflict retained both the newer canonical ignore entries and the topic build-output exclusions.

Maintenance triage (2026-09-29)

Disposition: active canonical Ubuntu modernization; draft until split into reviewable patches.

Maintenance need: the Vibe server has a reproducible Ubuntu 26/OpenJDK 11 build and uses maintained system image libraries so current GPU/userspace packages can coexist with SageTV. The stack passes Java/native builds, JNI/ELF checks, generated ImageLoader fixtures, malformed-input containment, packaging, startup, and repeated shutdown in that environment.

This remains too broad for maintenance merging as one stack: it combines compiler changes, native dependency policy, ImageLoader behavior, packaging, and a new development environment. The newer-Ubuntu requirement is not Vibe-only and is not being withdrawn. Upstream must decide its supported Linux, Windows, and macOS native-library matrix, then review independently justified compiler, ImageLoader, native-library, and reproducible-build changes.

Current-Ubuntu container dependency

This draft contains the current-Ubuntu build, ImageLoader/system-library, validation, and media-utility pieces needed to prove canonical SageTV on a current base. It follows #528 and is independent of #516 (launcher) and #519 (source-clean build). It should be split into reviewable Core changes before a separate OpenSageTV/sagetv-dockers PR proposes the non-root runtime image, supervisor, packages, health checks, and GPU device mappings. The future container PR must pass with stock Core plus these proposed patches as well as with Vibe Core.

Scope clarification after review

Repository-wide line-ending policy is excluded from this draft. The previously included five-line .gitattributes file has been removed; any line-ending change must be justified independently by a reproduced failure and reviewed separately.

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