feat: add replace subcommand with multi-pattern support

specs/002-add-replace-command/research.md

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+# Phase 0 Research: Replace Command with Multi-Pattern Support
+
+## Decision: Literal substring replacement with ordered evaluation
+- **Rationale**: Aligns with current rename semantics and keeps user expectations simple for first
+  iteration; avoids complexity of regex/glob interactions. Ordered application ensures predictable
+  handling of overlapping patterns.
+- **Alternatives considered**:
+  - *Regex support*: powerful but significantly increases validation surface and user errors.
+  - *Simultaneous substitution without order*: risk of ambiguous conflicts when one pattern is subset
+    of another.
+
+## Decision: Dedicated replace service under `internal/replace`
+- **Rationale**: Keeps responsibilities separated from existing listing module, enabling reusable
+  preview + apply logic while encapsulating pattern parsing, summary, and reporting.
+- **Alternatives considered**:
+  - *Extending existing listing package*: would blur responsibilities between read-only listing and
+    mutation workflows.
+  - *Embedding in command file*: hinders testability and violates composable rule principle.
+
+## Decision: Pattern delimiter syntax `with`
+- **Rationale**: Matches user description and provides a clear boundary between patterns and
+  replacement string. Works well with Cobra argument parsing and allows quoting for whitespace.
+- **Alternatives considered**:
+  - *Using flags for replacement string*: more verbose and inconsistent with provided example.
+  - *Special separators like `--`*: less descriptive and increases documentation burden.
+
+## Decision: Conflict detection before apply
+- **Rationale**: Maintains Preview-First Safety by ensuring duplicates or invalid filesystem names are
+  reported before commit. Reuses existing validation helpers from rename pipeline.
+- **Alternatives considered**:
+  - *Best-effort renames with partial success*: violates atomic undo expectations.
+  - *Skipping conflicting files silently*: unsafe and would erode trust.