refactor(hashline-edit): remove HASHLINE_LEGACY_REF_PATTERN and legacy ref compat

Remove the old LINE:HEX (e.g. "42:ab") reference format support. All
refs now use LINE#ID format exclusively (e.g. "42#VK"). Also fixes
HASHLINE_OUTPUT_PATTERN to use | separator (was missed in PR #2079).

src/tools/hashline-edit/validation.test.ts

@@ -61,46 +61,3 @@ describe("validateLineRef", () => {
       .toThrow(/>>>\s+2#[ZPMQVRWSNKTXJBYH]{2}\|two/)
   })
 })
-
-describe("legacy LINE:HEX backward compatibility", () => {
-  it("parses legacy LINE:HEX ref", () => {
-    //#given
-    const ref = "42:ab"
-
-    //#when
-    const result = parseLineRef(ref)
-
-    //#then
-    expect(result).toEqual({ line: 42, hash: "ab" })
-  })
-
-  it("parses legacy LINE:HEX ref with uppercase hex", () => {
-    //#given
-    const ref = "10:FF"
-
-    //#when
-    const result = parseLineRef(ref)
-
-    //#then
-    expect(result).toEqual({ line: 10, hash: "FF" })
-  })
-
-  it("legacy ref fails validation with hash mismatch, not parse error", () => {
-    //#given
-    const lines = ["function hello() {"]
-
-    //#when / #then
-    expect(() => validateLineRef(lines, "1:ab")).toThrow(/>>>\s+1#[ZPMQVRWSNKTXJBYH]{2}\|/)
-  })
-
-  it("extracts legacy ref from content with markers", () => {
-    //#given
-    const ref = ">>> 42:ab|const x = 1"
-
-    //#when
-    const result = parseLineRef(ref)
-
-    //#then
-    expect(result).toEqual({ line: 42, hash: "ab" })
-  })
-})