Fix lore command index handling and default-command typo

[dmccoystephenson]

Summary

• /pl edit and /pl remove now treat lineIndex as 1-based, matching COMMANDS.md/USER_GUIDE.md, instead of silently indexing 0-based into the lore list (following the documented example -- add one line, then /pl edit 1 ... -- previously threw an uncaught IndexOutOfBoundsException).
• Both commands now guard against missing/non-numeric index arguments with a player-facing message instead of throwing ArrayIndexOutOfBoundsException/NumberFormatException.
• DefaultCommand no longer tells players to type the non-existent /lp help; it now says /pl help, consistent with every other usage string in the plugin and plugin.yml's registered commands (pl, playerlore).
• Added JUnit 5 + Mockito as the project's first test dependencies (none existed previously) and added tests covering the fixed paths in EditCommand, RemoveCommand, and DefaultCommand.
• Documented all three fixes in CHANGELOG.md under [Unreleased].

Test plan

• mvn compile -- clean
• mvn test -- 11/11 passing
• Empirical regression check: stashed the fix, re-ran the new tests, confirmed 9 of them fail (ArrayIndexOutOfBounds, NumberFormatException, wrong-index assertions), then restored the fix and confirmed all 11 pass again
• Docs (COMMANDS.md, USER_GUIDE.md) already described the correct (1-based) behavior -- no doc changes needed, only the code was brought in line with them

Closes #7
Closes #8

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This PR description was drafted during a Gardener session (Stephenson-Software/gardener).

[dmccoystephenson]

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This comment was drafted during a Gardener session (Stephenson-Software/gardener).

[dmccoystephenson]

Self-review rubric:

• Scope: PASS -- every changed file is necessary for DefaultCommand tells players to type /lp help instead of /pl help #7 (DefaultCommand.java typo, CHANGELOG.md) or EditCommand/RemoveCommand use 0-based lineIndex but docs/UX imply 1-based, and reject bad input ungracefully #8 (EditCommand.java/RemoveCommand.java validation+indexing fix, pom.xml test deps, CHANGELOG.md), plus the tests that exercise them. No unrelated files touched.
• Tests-new: PASS -- EditCommandTest, RemoveCommandTest, and DefaultCommandTest each exercise the changed execute() paths (1-based edit/remove, out-of-range index, non-numeric index, missing args, and the corrected /pl help string).
• Tests-fix: PASS (empirical) -- stashed EditCommand.java/RemoveCommand.java/DefaultCommand.java, re-ran mvn test: 9 of 11 tests failed as expected (ArrayIndexOutOfBoundsException, NumberFormatException, wrong-index assertions, wrong help string). Restored the fix, re-ran: 11/11 pass.
• Sibling structure: PASS -- the three new test files live under src/test/java/dansplugins/playerlore/commands, mirroring the main source package, and follow <ClassName>Test.java naming (no prior test files existed to compare against, so this establishes the convention).
• Sibling renames: N/A -- no identifier renames in this PR.
• Docs: PASS -- COMMANDS.md and USER_GUIDE.md already documented lineIndex as 1-based; no doc edits were needed since the code was the thing that was wrong, not the docs. CHANGELOG.md [Unreleased] now has a Fixed section describing all three fixes.
• Issue resolution: PASS -- DefaultCommand tells players to type /lp help instead of /pl help #7's exact string (/lp help -> /pl help) is changed; EditCommand/RemoveCommand use 0-based lineIndex but docs/UX imply 1-based, and reject bad input ungracefully #8's named surface (EditCommand/RemoveCommand lineIndex handling) is changed in both files with matching validation.
• CI: PASS -- green on head commit f45565d (https://github.com/Dans-Plugins/PlayerLore/actions/runs/30770764974).

Repo-specific:

• Command trio parity: PASS -- EditCommand and RemoveCommand (the two of the trio that take a lineIndex) now use identical guard/try-catch/1-based-bounds logic. AddCommand doesn't take an index argument, so no equivalent change applies there.

No open judgment-call items -- all rubric items pass with direct evidence.

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This comment was drafted during a Gardener session (Stephenson-Software/gardener).

[dmccoystephenson]

Holding this PR for manual merge rather than auto-merging: it modifies `pom.xml` (adding `junit-jupiter`/`mockito-core` as test-scope dependencies, plus an explicit `maven-surefire-plugin` version), which is on this repo's do-not-auto-merge list because pom.xml changes affect the shaded JAR/release artifact. The added dependencies are test-scope only (excluded from the shade plugin) so they should not affect the release artifact, but per this skill's own rule a pom.xml match requires human sign-off rather than autonomous merge, regardless of the broader merge pre-authorization for this run.

CI is green (https://github.com/Dans-Plugins/PlayerLore/actions/runs/30770764974) and the self-review rubric above passed with no open judgment calls. Ready to merge on approval.

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This comment was drafted during a Gardener session (Stephenson-Software/gardener).