Add pluggable movement strategies (v1.3.0)

Turn the hardcoded straight-line sweep into a strategy system behind three
seams so new patterns are easy to add and, for the first time, testable
without nut.js or a real screen:

- src/device.ts:     injectable Device seam over nut.js (autoDelayMs lives
                     here now); the only module that touches the native lib.
- src/strategies.ts: pure per-pattern path generators + registry + lenient
                     name resolution. Ships line, diagonal, jitter, walk,
                     arc, figureEight.
- src/executor.ts:   single executePath driver owning bounds policy
                     (abort/clamp/reflect), pacing, interrupt detection, and
                     restore-on-clean.

keeper.ts's simulateActivity now selects a strategy and delegates to the
executor; the default `line` pattern is byte-for-byte the previous behavior.

New config surface, layered CLI > file > default with strict validation:
- -p/--pattern <name>   movement strategy (names matched case/-/_-insensitive)
- -s/--step-size <px>   pixels per step; stepCount is now a step *count*

Robustness for the new edge-seeking patterns: interrupt detection compares
against the last commanded (rounded) point with a 2px tolerance, and
clamp/reflect stay a couple pixels off the screen edge, so sub-pixel cursor
placement on scaled/multi-monitor displays isn't misread as user activity.
jitter's radius scales with sweep length so it moves at the default stepSize.

Tests: new suites for strategies, the executor (all bounds policies,
rounding, interrupt, tolerance, pacing), and the keeper loop; config and
configFile suites extended for pattern/stepSize. editor.test.ts moved to
tests/ for consistency. 64 pass.

src/configFile.ts

@@ -10,7 +10,9 @@
  *   moveInterval   number   seconds, positive
  *   checkInterval  number   seconds, positive
  *   stepDelay      number   milliseconds, positive
- *   stepCount      number   pixels, positive
+ *   stepCount      number   count, positive
+ *   stepSize       number   pixels, positive
+ *   pattern        string   a registered strategy name
  *   verbose        boolean
  *
  * Unknown keys, wrong types, and non-positive numerics are rejected with a
@@ -29,12 +31,15 @@ import { existsSync, readFileSync, statSync } from "node:fs";
 
 import { defaultConfigPath, type ConfigOverrides } from "./config.ts";
 import { CliError } from "./errors.ts";
+import { PATTERN_NAMES, resolvePatternName } from "./strategies.ts";
 
 const ALLOWED_KEYS: ReadonlySet<string> = new Set<string>([
     "moveInterval",
     "checkInterval",
     "stepDelay",
     "stepCount",
+    "stepSize",
+    "pattern",
     "verbose",
 ]);
 
@@ -60,6 +65,16 @@ function requireBoolean(name: string, raw: unknown, path: string): boolean {
     return raw;
 }
 
+function requirePatternName(name: string, raw: unknown, path: string): string {
+    const canonical: string | null = typeof raw === "string" ? resolvePatternName(raw) : null;
+    if (canonical === null) {
+        throw new CliError(
+            `invalid value for '${name}' in ${path}: ${JSON.stringify(raw)} (valid: ${PATTERN_NAMES.join(", ")})`,
+        );
+    }
+    return canonical;
+}
+
 /**
  * Load and validate the config file. See module docstring for return
  * semantics.
@@ -130,6 +145,14 @@ export function loadConfigFile(explicitPath: string | undefined): ConfigOverride
             "stepCount" in parsed
                 ? requirePositiveNumber("stepCount", parsed.stepCount, path)
                 : undefined,
+        stepSize:
+            "stepSize" in parsed
+                ? requirePositiveNumber("stepSize", parsed.stepSize, path)
+                : undefined,
+        pattern:
+            "pattern" in parsed
+                ? requirePatternName("pattern", parsed.pattern, path)
+                : undefined,
         verbose:
             "verbose" in parsed
                 ? requireBoolean("verbose", parsed.verbose, path)