docs: fix factual errors across all documentation files

[tankdonut]

Summary

Systematic review and correction of all 20 audit findings across 8 documentation files. Every line of documentation was reviewed against actual source code and corrected where factual errors were found.

Changes

Critical Fixes (wrong information)

• Config paths: All references now correctly point to build/.opencode/opencode.json (root-level opencode.json does not exist)
• Plugin list: Replaced fabricated plugins (ecc-universal, oh-my-opencode, unpinned versions) with actual pinned versions from source (@tarquinen/[email protected], [email protected], [email protected])
• Container base image SHA: Removed outdated SHA references, use tag-only ghcr.io/tankdonut/tools
• Fabricated container config: Replaced invented opencode.jsonc content (extends, containerMode, pluginConfig, agentSettings) with actual config from source
• Non-existent npm package: Removed all references to @opencode/cli — OpenCode installs via npm install -g opencode
• Fake CLI commands: Removed opencode list-plugins, opencode validate, opencode list-skills, opencode lint, opencode --config-check, opencode --trace-config

Structural Fixes (missing documentation)

• Project trees: Added missing .pre-commit-config.yaml, tests/, build/.opencode-checksums, scripts/bump-version.sh
• build.sh workflow: Replaced non-existent --version flag with actual bump-version.sh workflow

Minor Fixes

• Node.js version: Updated from 12.22+ to 20+ (matching CI)
• License: Fixed to MIT in README and CONTRIBUTING
• configuration.md: Completely rewritten from 586 lines of fabricated content to 211 lines based on actual config files
• usage.md: Removed speculative environment variables, fake commands, and --cache-from flag

Files Changed

File	Changes
AGENTS.md	Tree, plugins, SHA, version example
README.md	License → MIT
DEVELOPMENT.md	Paths, SHA, build workflow
CONTRIBUTING.md	License → MIT
docs/guides/installation.md	Tree, plugins, paths, SHA
docs/guides/installation-detailed.md	Node.js, npm package, paths, fake commands
docs/guides/usage.md	Fake commands, env vars, plugins, paths
docs/guides/configuration.md	Complete rewrite with actual config

214 insertions, 642 deletions across 8 files.

Verification

• ✅ Zero root-level opencode.json references remain
• ✅ Zero SHA references in documentation
• ✅ Zero fake CLI commands remain
• ✅ All plugin lists match actual build/.opencode/opencode.json
• ✅ All paths verified against source code
• ✅ Pre-commit hooks pass