Add progressive flashcard sessions

[backslash-f]

Summary

• add a deterministic, response-mode-agnostic progressive session for ordered flashcard stages
• select a fixed number of distinct cards by canonical identity and seeded shuffle
• promote, retain, complete, and tail-requeue cards through monotonic session-scoped attempts
• reject invalid, future, stale, and post-completion submissions before mutating session state
• expose separate selected-card, completed-card, and generated-attempt progress dimensions
• add privacy-safe progressive lifecycle logs without card, stage, attempt, prompt, answer, or asset values
• document progression semantics and retain the existing finite stage-zero ThreeChoiceSession unchanged

Validation

• AgentGuidelines/Scripts/swift_format.sh format-and-lint Package.swift Sources Tests
• AgentGuidelines/Scripts/swift_format.sh lint-strict Package.swift Sources Tests
• swift build
• swift test — 46 test declarations / 59 parameterized executions, zero failures
• swift package generate-documentation --target FlashcardKit --disable-indexing --output-path <temporary-path> --transform-for-static-hosting --hosting-base-path flashcardkit
• AgentGuidelines/Scripts/validate_consumer_setup.swift --consumer-root . --require-swift-format
• AgentGuidelines/Scripts/validate_guidelines.swift AgentGuidelines
• swift package dump-package — Swift 6 language mode plus warning/error and required upcoming-feature settings verified for both local targets
• .agents/skills/agent-guidelines-audit/scripts/check_markdown_wrapping.swift README.md AGENTS.md Sources/FlashcardKit/FlashcardKit.docc
• git diff --check
• AgentGuidelines subtree tree b40e2c75de8681ade6a5ae97ad3ddd8a28f3adda exactly matches tag 0.0.34
• merged FK-1 base tree exactly matches its reviewed head tree 2cc2aca77a91a178906254680ab11a8b5168a499

Audit notes

• No dependency graph, deterministic RNG, three-choice API, UI, language-specific, or pronunciation changes.
• Progressive logging retains FlashcardKit's registered 🃏 identity and com.thatfactory.flashcardkit subsystem.