daemon/rule: stop mutating regex Data field on Compile (#1587)

[tredondo]

Fixes #1587.

Compile() for Regexp operators with Sensitive==false used to do

o.Data = strings.ToLower(o.Data)

before compiling the pattern. That works as an ASCII-only way to make matching case-insensitive (pattern and subject both lowercased), but it mangles the pattern string itself. A regex like [0-9A-Za-z]+ becomes [0-9a-za-z]+: still valid, but visibly wrong, and the mangled value then bleeds into:

• the rule JSON written to disk by loader.Save (json.MarshalIndent serializes the post-Compile o.Data)
• the GUI display of the operator data and the slugified rule name

This is most visible on the auto-generated rules for AppImages, whose process.path lives under /tmp/.mount__/, producing the [0-9a-za-z]+ duplication the user can see in the popup and on disk.

Switch to Go regexp's native case-insensitivity instead: prepend the (?i) flag to a local pattern string and compile that. o.Data is no longer touched by Compile, so the original pattern survives both serialization and the round-trip back to the UI. reCmp can drop its matching strings.ToLower(data) call, since the compiled regex now handles case folding itself.

Existing rules on disk that already have a lowercased pattern keep working: (?i) over a [0-9a-z]+-style class is equivalent to the previous lowercase-both-sides behavior, and case-sensitive rules are unaffected (no (?i) is added).

A regression test (TestNewOperatorRegexpDataNotMutated) pins both the pattern-preservation contract and case-insensitive matching against an appimage-style path.