Fix string method dispatch misrouting to effects by value content

[jaimeam]

Problem

Calling a method on a string literal whose content began with an effect/capability name (Net, Fs, Console, Clock, Rand, Env, Map, Set) misrouted the call to that effect, throwing at runtime (E4004/E4006) — even though astra check reported no errors.

"Netback".to_lower()   // [E4004] capability not available: Net
"Console".to_lower()   // [E4006] unknown method: Console.to_lower
"Coke".to_lower()      // OK

Root cause

Effect namespaces and ordinary strings shared the Value::Text representation. call_method decided "is this an effect?" by inspecting the string's content (name.starts_with("Net")), so any Text value spelling an effect name got hijacked.

Fix

New Value::Effect(String) variant so method dispatch keys off the receiver's type, never its string value. Effect identifiers evaluate to Value::Effect; call_method reaches an effect handler only for Value::Effect receivers (exact-name match). Every other receiver — including all Value::Text — resolves by type via call_value_method.

Tests

• 3 regression tests: every string method, every effect name as a prefix, exact-match strings, previously-passing cases, and confirmation real effect identifiers still dispatch.
• Full suite: 396 passed, 0 failed.

Also

• Documents decision in ADR-008.
• Fixes 6 pre-existing clippy lints (sort_by_key, collapsible match guards in lsp/typechecker) so pre-commit passes without --no-verify.

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