style: use ASCII punctuation in new prompt/doc/test prose

This branch's new content used em-dashes and a Unicode "<=" sign in a
few places (opsx-explore.prompt.md, opsx-onboard.prompt.md, AGENTS.md,
VersionInfoProviderTests.cs), which render poorly in some git tooling.
Switch them to the ASCII "--" and "<=" forms the rest of the repo's
prose and comments already use.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: johnml1135

.github/prompts/opsx-explore.prompt.md

@@ -6,4 +6,4 @@ argument-hint: "What to explore: an idea, problem, change name, or nothing"
 
 Use the `openspec-explore` skill from `.claude/skills/openspec-explore/SKILL.md`.
 
-Treat any text supplied with this prompt as the starting point for exploration — a vague idea, a specific problem, a change name, or nothing.
+Treat any text supplied with this prompt as the starting point for exploration -- a vague idea, a specific problem, a change name, or nothing.

.github/prompts/opsx-onboard.prompt.md

@@ -5,4 +5,4 @@ agent: "agent"
 
 Use the `openspec-onboard` skill from `.claude/skills/openspec-onboard/SKILL.md`.
 
-The skill will guide through a complete OpenSpec cycle — explore, new change, propose, apply, archive — using a real task from the codebase with narration at each step.
+The skill will guide through a complete OpenSpec cycle -- explore, new change, propose, apply, archive -- using a real task from the codebase with narration at each step.

AGENTS.md

@@ -8,8 +8,8 @@ Minimal, high-signal guidance for coding agents in this repository.
 - Build with `.\build.ps1`.
 - Test with `.\test.ps1`.
 - Do not bypass repository scripts for normal build/test work.
-- Commit messages are linted by CI (gitlint, `.gitlint`): title ≤72 chars,
-	body lines ≤80 chars. Check with `gitlint --commits origin/main..HEAD`
+- Commit messages are linted by CI (gitlint, `.gitlint`): title <=72 chars,
+	body lines <=80 chars. Check with `gitlint --commits origin/main..HEAD`
 	before pushing.
 
 ## Critical constraints

Src/Common/FwUtils/FwUtilsTests/VersionInfoProviderTests.cs

@@ -13,7 +13,7 @@ namespace SIL.FieldWorks.Common.FwUtils
 	/// How versions and copyrights are read out of the generated version attributes
 	/// (CommonAssemblyInfo.cs, generated from CommonAssemblyInfoTemplate.cs + MasterVersionInfo.txt).
 	/// This test assembly links the generated file, so these tests run against the real attribute
-	/// shapes the product ships — including the empty-FWBETAVERSION informational version
+	/// shapes the product ships -- including the empty-FWBETAVERSION informational version
 	/// ("9.x.y.NNNNN NNNNN " with a trailing space).
 	/// </summary>
 	[TestFixture]