feat(eval): add replay eval command, action fingerprints, and delta scoring (closes #14)

[theonly1me]

What changed

• Implement shadowclone eval command with --sessions, --since, --json, and --max-budget-usd flags.
• Record action fingerprints in EngineRun from stream-json parsing without capturing prompt or tool payloads.
• Normalize file paths to repository-relative posix paths in replay evaluation.
• Exclude empty dimensions from the similarity mean and report per-dimension deltas between clone and baseline.
• Persist evaluation receipts to ~/.shadowclone/eval/<evalId>.json for reproducible replication.
• Document privacy-safe action representation principles in docs/design/eval-representation.md.

Why

Measuring whether cloned profiles reproduce developer behavior requires reproducible, falsifiable metrics. Comparing clone replays against an unprofiled baseline isolates the profile's true behavioral lift from shared agent base rates. Action fingerprints prevent evaluating full tool inputs that could re-expose sensitive code or secrets.

How to verify

bun run typecheck
bun test
bun run check

Data handling

• Any new capture source has an opt-in flag and a README entry in this PR
• Everything that reaches the network passes redactSecrets
• No raw capture in a log line, an error message, or a test fixture
• A test exercises the real entry point, not just the redaction function

[theonly1me]

Suggested change

	for (let i = 0; i < arguments_.length; i++) {
	const arg = arguments_[i];
	if (arg === "--json") {
	for (let argumentIndex = 0; argumentIndex < arguments_.length; argumentIndex++) {
	const argument = arguments_[argumentIndex];
	if (argument === "--json") {

[theonly1me]

Spawning 40 unattended agent runs without a cost preview can burn user budget unexpectedly. We should print the upper bound cost and prompt for confirmation when running interactively.

[theonly1me]

Running both the baseline and clone directly in os.tmpdir() means they share the machine's top-level temp dir. We should run each in an isolated mkdtemp folder and clean it up after the session finishes.