Add text UI tick-speed toggle and guard -1 location lookups

[dmccoystephenson]

Summary

• The text UI's handleKeyDownEvent was missing the l key case present in the pygame branch, so --text-ui players had no way to toggle config.limitTickSpeed even though README documents the control generically. Added the case and updated TextRenderer.renderControls() to mention it.
• Ophidian.getLocation() now guards against a locationID that isn't a real grid location (e.g. an entity's default -1 sentinel from Entity.__init__) instead of letting Grid.getLocation() raise an unhandled KeyError. movePreviousSnakePart() now returns immediately after quitApplication() instead of falling through to use a location that was never fetched.

Test plan

• python -m pytest — 91 passed
• New regression test test_text_ui_l_key_toggles_tick_speed_limit covers the text UI l key handling

Closes #101
Closes #22

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

[dmccoystephenson]

Self-review: both fixes are narrowly scoped and verified against source. getLocation()'s guard directly addresses issue #22 (an entity's default -1 locationID sentinel from Entity.__init__ would otherwise hit Grid.getLocation()'s raw dict lookup and raise KeyError), and the added return after quitApplication() in movePreviousSnakePart prevents falling through to use snakePart.lastPosition on the error path. The text UI l key case mirrors the existing pygame branch exactly and is covered by a new regression test; TextRenderer.renderControls() was updated to match, closing the graphical/text UI drift called out in issue #101 (and past PR #92/#95/#99 review feedback). 91/91 tests pass locally.

One pre-existing rough edge, not introduced by this PR and left out of scope (outside both linked issues): removeEntityFromLocation (src/ophidian.py:392) calls self.getLocation(entity) then location.isEntityPresent(entity) without checking for the -1 sentinel this PR's guard can now return. That was already an unhandled crash path before this change (previously KeyError from Grid.getLocation, now AttributeError on -1.isEntityPresent) — a candidate for the same guard if a future issue surfaces a real crash there.

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