chore(release): prepare 0.16.0 + seed the Conan Center recipe at 0.16.0

[facontidavide]

Summary

Repurposes this PR (was: pin the CCI recipe to v0.15.0) into the 0.16.0 release-prep PR. Rebased on main so it sits on top of #144.

Version bump 0.15.0 → 0.16.0 (MINOR). Covers #144, which removed the host-side PluginRuntimeCatalog (moved to the app, pj_runtime). No plugin links it and abi/baseline.abi is unchanged (verified: empty diff since v0.15.0), so per the plugin-impact rule this is not a MAJOR — but it does remove host-facing public API, which is exactly why the CCI seed moves to 0.16.0: whatever version CCI accepts first becomes the floor consumers pin against, and seeding 0.15.0 would publish API that 0.16.0 removes.

Changes

• Version sources → 0.16.0: conanfile.py, PJ_PACKAGE_VERSION in CMakeLists.txt, context.version in recipe.yaml, + the conanfile docstring example (the set the conda-release.yml tag-verify job checks).
• CHANGELOG.md: adds the [0.16.0] entry for refactor(plugins): move the duplicate-resolution catalog to the host #144, and relabels the per-topic-pause section from [Unreleased] to [0.15.0] — it shipped in the v0.15.0 tag but the changelog was never relabeled.
• CCI recipe re-seeded at 0.16.0: config.yml, conandata.yml, README (rationale, conan create commands, CCI PR title).
• Bug fix (leftover from refactor(plugins): move the duplicate-resolution catalog to the host #144): pj_plugin_runtime_catalog was still declared in the plugin_host component libs of both the root conanfile.py and the CCI recipe. The library no longer exists, so any conan create/consume of the package would break. Removed from both.

The tag ↔ sha256 chicken-and-egg

The digest of the v0.16.0 tag tarball cannot exist before the tag is cut (and the tarball contains conandata.yml, so the true digest can never be embedded in the tag itself). Resolution: conandata.yml ships an explicit all-zeros placeholder sha256 with a loud comment, and the README gains an "After tagging v0.16.0" section with the one-liner to recompute it. The in-repo tree is only staging — the authoritative copy is the one pasted into the conan-center-index fork after the tag exists.

Release flow after merge

1. Merge this PR.
2. Tag v0.16.0 on the merge commit and push the tag (release workflow verifies tag == all three version sources).
3. curl -sL .../v0.16.0.tar.gz | sha256sum → replace the placeholder in conandata.yml (one-line follow-up commit on main).
4. Copy packaging/conan-center-index/recipes/plotjuggler_sdk/ into the CCI fork and open plotjuggler_sdk/0.16.0.

Testing

• ./build.sh --debug (Debug+ASAN) — passes.
• ./test.sh — 49/49 pass.

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