Track a general spec.coding-agent-lab.md variant-spec convention

[Carr1005]

Summary

• Add one .gitignore negation (!courses/*/spec.coding-agent-lab.md) so any course can carry a tracked variant of its canonical spec.md, without a per-experiment .gitignore edit. Update CLAUDE.md and README.md's version-control notes to match.
• Ships the agent-memory course's first use of this convention: courses/agent-memory-building-memory-aware-agents/spec.coding-agent-lab.md removes Oracle AI Database as a selectable build-time Options entry in Decision Ledger rows D14 (persistent store) and D5 (environment) — while keeping the course's actual use of Oracle as provenance elsewhere in the spec (§1 Not Included, §2's honest pins note, CTX-D), per the generation guide's ground-truth/honesty rule.
• No other Ledger row, business rule, or acceptance criterion depends on Oracle — confirmed by full-file audit before editing; the spec's default was already SQLite, so this only removes a choice, not the build target.

Test plan

• git status shows the variant file tracked (previously invisible under the blanket courses/*/* ignore)
• diff against the canonical spec.md touches only the 2 Ledger cells + a new provenance blockquote note — everything else byte-identical
• Next /generate-spec or /prepare-build run on any course still resolves spec.md unambiguously (no skill globs spec*.md)

🤖 Generated with Claude Code