feat: parse Insert from URL script step

[bc-m]

Summary

Fixes #191.

The "Insert from URL" step (id 160) wraps its URL parameter in
<Parameter type="URL"><URL autoEncode="…"><Calculation>…. There was no
handler for the URL parameter type, so the step rendered a
⚠️ PARAMETER "URL" NOT PARSED ⚠️ placeholder and dropped the URL calc.

This adds a dedicated insert_from_url step module (mirroring insert_text),
dispatched from sanitizer.rs, and registers InsertFromURL = 160 in the
ScriptStep enum.

Rendering

Fields are emitted in FileMaker's option order:

Insert from URL [ Select ; With dialog: OFF ; Target: $response ; URL: $url ; Verify SSL Certificates ; cURL options: $curlOptions ]

• URL is parsed from the doubly-nested <Calculation> and rendered as URL: <calc>.
• cURL options (the trailing type="Calculation") is prefixed with cURL options:.
• Select and Verify SSL Certificates are shown by name only when enabled, omitted when off. These are keyed by parameter id (4096 / 268435456), so the behavior also holds for localized exports (e.g. Auswahl, SSL-Zertifikate verifizieren).
• Verify SSL Certificates is repositioned to just before cURL options.
• The autoEncode attribute is intentionally not surfaced.

Test plan

• New unit tests in insert_from_url.rs (empty URL, full step, Select/Verify off)
• cargo test — 118 passing
• cargo clippy --all-targets clean, cargo fmt applied
• Snapshots regenerated; every changed line verified to be an Insert from URL step (English + German fixtures), nothing else touched

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