fix(session): unify JSONL persistence and continuation rotation

[M09Ic]

Summary

• make *aop.Event the only durable event structure and append it through one App EventBus subscriber as AOP ProtoJSONL
• persist agent, direct scan, and scanner-native tool artifacts (including gogo results) through that same stream
• remove checkpoint/snapshot input, ToolDataEvent, ToolArtifact, ArtifactStream, TimelineWriter, timeline parsing, and resume replay/fork pipelines
• keep progress ephemeral and keep -F as direct AOP JSONL presentation; structured artifact payloads are not converted to Markdown
• use canonical aop.tool.Artifact / aop.tool.Progress with call_id correlation (depends on feat(aop): correlate tool artifacts and progress cyber-ui#10)

Session semantics

• -f <path>: stream agent, scan, and artifact AOP events to exactly that JSONL file
• --save-session: auto-select .aiscan/sessions/session-*.jsonl; REPL mode records automatically
• -r <path>: restore the latest root-agent continuation and append new events to the same file
• -r and -f are mutually exclusive; -r may coexist with --save-session and wins
• /clear: end with cleared and create an empty continuation in the current file
• /compact: end with compacted and create a continuation containing the compacted context in the current file
• /resume <path>: when idle, end the current session with resumed, switch the recorder to the target file, and create the continuation there
• rotation commands reject active runs with /stop guidance
• child-agent sessions with parent_tool_call_id are excluded from root resume selection

Validation

• go test ./...
• go test -tags full ./cmd/aiscan ./examples/acp/server ./tools ./tools/katana
• go test -race ./core/output ./pkg/runner ./pkg/node ./tools/scan
• real WSL tmux REPL validation for /clear, /resume, /compact, session parent links, file switching, and end reasons
• real CLI validation for explicit -f, same-file -r append, -F Markdown rendering, and -r/-f conflict

Dependency: chainreactors/cyber-ui#10