refactor: reorganize demo tooling under content/demo hub

[Andreas-Garcia]

Description

Reorganizes library demo tooling under a single content/ hub, replacing the old docs/demos/ and root-level scripts/demo_repl.py / scripts/run_demo_tape.py:

• content/demo/: hub for library demo docs (docs/), demo scripts (scripts/), and shared tapes/output (demos/).
• content/scripts/: content build scripts that aren't demo-specific.
• Drops the old top-level content/linkedin/ channel-folder convention, superseded by per-article platform subfolders (see content/README.md).

Picked up along the way:

• run_demo_tape.py's repo_root resolution was one directory level too shallow, so content/articles/ was never found — fixed the .parent chain.
• Both library demo tapes and their README cd'd only two levels up instead of three, breaking repo-root-relative paths.
• run_demo_tape.py rewrote a tape's Output ... directive with re.sub() without checking a replacement occurred — now uses re.subn() and errors if nothing matched.
• system-dependencies-demo.toml's install comment referenced a nonexistent Ubuntu install script.

Split out of #80 — this is the infra move that #80's new article content builds on top of.

Type of Change

• Code refactoring (no functional changes)
• Bug fix (non-breaking change which fixes an issue)

Pre-PR Checklist

• Ran pre-commit hooks (all passed except verify-system-dependency-versions, skipped locally — pinned mediainfo version is bumped in fix(ci): bump macOS mediainfo pin 26.01 -> 26.05 #81, unrelated to this PR's content)

[Copilot]

Pull request overview

This pull request reorganizes demo/content tooling into a centralized content/ hub, migrating the previous docs/demos/ and root scripts/*demo* utilities into content/demo/, and updating docs/config to match the new layout.

Changes:

• Move demo scripts and VHS demo docs into content/demo/ and remove legacy docs/demos/ + scripts/run_demo_tape.py.
• Add new library demo tapes under content/demo/demos/tapes/ and supporting installation/docs under content/demo/docs/.
• Update repo docs and configs (AGENTS.md, .cursor/rules/*, pyproject.toml, .gitignore, pre-commit excludes, CHANGELOG.md) to reflect the new structure and behavior.

Reviewed changes

Copilot reviewed 26 out of 28 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
system-dependencies-demo.toml	Updates install comments to reflect the new demo tooling layout and removes reference to a nonexistent Ubuntu script.
scripts/run_demo_tape.py	Removes legacy tape runner script under scripts/.
pyproject.toml	Updates Ruff per-file ignores to point to demo scripts under content/demo/scripts/.
docs/demos/tapes/get_full_metadata.tape	Removes legacy doc demo tape.
docs/demos/README.md	Removes legacy demo documentation under docs/demos/.
content/scripts/README.md	Adds documentation for non-demo content scripts and points to new demo tooling locations.
content/README.md	Replaces old “channel folder” convention with the new content/demo, content/scripts, and content/articles structure.
content/linkedin/2025-02-example-draft/.gitkeep	Removes legacy LinkedIn draft scaffolding.
content/linkedin/2025-02-example-draft.md	Removes legacy LinkedIn draft scaffolding.
content/linkedin/2025-02-audiometa-1.0.0-draft.md	Removes legacy LinkedIn draft content.
content/demo/scripts/run_demo_tape.py	Adds new article-oriented tape runner that selects recent tapes and rewrites Output robustly.
content/demo/scripts/install-demo-dependencies-macos.sh	Adds macOS installer for VHS demo dependencies.
content/demo/scripts/demo_repl.py	Adds REPL-style demo script used by VHS tapes.
content/demo/scripts/article_output_paths.sh	Adds shared bash helpers for resolving article output paths.
content/demo/README.md	Adds a top-level README describing the content/demo hub structure.
content/demo/docs/VHS_DEMO_README.md	Adds detailed VHS demo usage/install documentation under the new location.
content/demo/docs/DEMO_VIDEOS_README.md	Adds demo video overview/reference under the new location.
content/demo/docs/DEMO_INSTALLATION.md	Adds install/troubleshooting guide for demo video creation under the new location.
content/demo/demos/tapes/audiometa_demo.tape	Adds library REPL-style VHS tape under the new layout.
content/demo/demos/tapes/audiometa_demo_script.tape	Adds library script-style VHS tape under the new layout.
content/demo/demos/README.md	Adds README for running library VHS demos from the new location.
CHANGELOG.md	Adds [Unreleased] entries documenting the demo tooling fixes and layout changes.
AGENTS.md	Updates contributor instructions for demo videos to the new content/demo + content/articles structure.
.pre-commit-config.yaml	Expands check-added-large-files exclude to include article sample audio directory.
.gitignore	Switches ignore rules from docs/demos to content/**/output/ and article-generated media patterns.
.cursor/rules/demo-videos.mdc	Updates Cursor rule guidance for demo videos to the new content layout and workflow.
.cursor/rules/demo-tape-authoring.mdc	Updates tape authoring guidance to match the new article/demo layout and conventions.
.cursor/rules/code-style.mdc	Updates demo-script carve-out paths to the new content/demo/scripts/* locations.

Suppressed comments (1)

content/demo/docs/DEMO_INSTALLATION.md:131

• This quick-test command uses a multi-line string with echo "... which will break when copied into a shell (the quote is not closed on the first line). Use printf (or a here-doc) to emit a valid multi-line tape to stdin.

# Test VHS (quick test)
echo "Output test.gif
Type 'echo Hello, World!'" | vhs /dev/stdin

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