fix(images): add indentContinuation ledger and sanitize inline fields (closes #552)

[xsvm]

Closes #552.

Summary

Establishes a bidirectional AST call-site ledger for indentContinuation, replaces safeTerm with safeTermSingle across 8 inline positions in images.go to prevent newline row forgery, and expands the #393 anti-corruption harness to guard safeTermSingle.

Key Changes

Area	Changes
Sanitizer	Added safeTermSingle (strings.ReplaceAll(safeTerm(s), "\n", " ")) in internal/cmd/safeterm.go.
Inline Fields	Applied safeTermSingle to 8 fields (Model, Sampler, CfgScale, Steps, Seed, URL, Username, NSFWLevel, and resources[].type/name/weight/hash) in internal/cmd/images.go.
AST & Behaviour	Added internal/cmd/indentcontinuation_ledger_test.go with TestIndentContinuationCallSitesAreLedgered (StructuralLedger pins 6 sites; BehaviouralSeam asserts zero \n leaks across all 8 fields + resources).
#393 Hardening	Extended internal/cmd/safeterm_userinput_test.go to audit both safeTerm and safeTermSingle (152 calls across 67 files verified).
Docs	Documented prompt indent vs wrap rationale in README.md.

Verification

# Closing gate
go test -count=1 ./internal/cmd -run Ledger
# PASS: TestIndentContinuationCallSitesAreLedgered (0.03s)
# PASS: 13 ledger tests (0.622s, exit code 0)

# #393 User-input guard (152 call sites audited)
go test -v -count=1 ./internal/cmd -run TestSafeTermIsNeverAppliedToUserTypedInput
# PASS: TestSafeTermIsNeverAppliedToUserTypedInput (0.03s)

# Regression & Lint
go test -v -count=1 ./internal/cmd -run TestREADMEAnchorLinksResolve
go test -v ./internal/cmd -run TestImages
gofmt -s -l . && go vet ./internal/cmd