Lean on Humanizer for standard string helpers; drop duplicates

**Tier 2 — Consolidate.** `src/Fallout.Utilities/Text/String.*` (~250 LOC) includes helpers that overlap [**Humanizer**](https://www.nuget.org/packages/Humanizer) — **already referenced** (v3.0.1): `String.Capitalize.cs` (→ `Pascalize`/`Transform`), `String.Truncate.cs` (→ `Truncate`), `String.Indent.cs`.

### Action
Delegate the standard string ops to Humanizer; delete the redundant helpers.

### Keep (domain-specific — do NOT delete)
- `String.Split.cs` + `String.KnownWords.cs` — camelCase/known-word splitting that drives CLI parameter naming. No Humanizer equivalent.
- `String.Quoting.cs` — build/CLI-specific quoting.

### ⚠️ Breaking change
Public extension methods → `breaking-change`, `experimental`, batched to yearly major, CHANGELOG migration note. `[Obsolete]` forwarders where practical.

### Acceptance
- [ ] `Capitalize`/`Truncate`/`Indent` delegate to or are replaced by Humanizer
- [ ] Domain-specific splitting/quoting retained
- [ ] CHANGELOG entry + migration note

_From dependency-consolidation audit, 2026-06-02._