changed: classify edits by place and parameters, not by name

[swapnilpaliwal-sd]

The per-declaration diff behind changed, test-impact and the edit hooks matched declarations by name and header text.

• A method renamed in place (same parameters, no overload keeping them) is now signature old — renamed old → new, targeted at the old declaration and its callers. Before, it was removed old + added new.
• JS/TS constructors are looked for as constructor(, not under the graph's <constructor> name. Before, every header edit was reported as removed + added S.constructor.
• Parameters are parsed by bracket depth. A destructured parameter is one row per field, defaults are compared, and a { inside the parameter list no longer ends the header.
• A function written inside another function's parameter list (a default value) is charged to the outer function. A file:line target that would resolve to a narrower callable on the same line falls back to the qualified name.
• this.x = … counts as declaring field x, so a field that is still assigned is not reported removed.
• A header that reappears word for word further down is reported as a move, not a signature change. When the graph already holds the new name, the old header is reported as renamed, not as a "return type".

Checked: new case javascript/edits-in-place (9 checks: 6 fail before the fix, all pass after). The rename checks in the python/java/csharp edit-targets-the-declaration-edited cases now require renamed X → Y. Case suites: JS 250/253, TS 176/181, Python 268/269, Java 304/304, C# 201/203; the failing checks are the same on the base branch. Engine JS suite 89/89. On the product: probes 47/70 on both builds, call edges 8960 = 8960, and a real rename gives the same 52 tests from the hook and the CLI.

• Rebased on 0.1.9: one name helper, header_name(n, d, rel) (how a declaration is spelled), used by both the range diff and this change; the header-text reader is now declared_name(h, is_py).
• Checked: 282/282 case checks (javascript + edit-targets in C#, Java, Python), edit_stale_spans 46/46, diff_verb ok; the new checks fail 9 of 28 on the base script.