Update app/lia_rules.py to add 18-month EOT outbound templates and the 18-month intro.

1. In app/lia_rules.py, define three new string constants:

EOT_18_NEW = (
    "Hi [customer_name], it’s Lia from Lincoln Audi.\n\n"
    "I’ve just been reviewing your account and you’re now around 18 months "
    "from the end of your agreement.\n\n"
    "This is a good time to carry out a quick end-of-warranty review so we can "
    "make sure everything is recorded correctly and that any potential warranty "
    "items are picked up while you're still fully covered.\n\n"
    "Once that’s done, I can also check whether there are any early upgrade "
    "benefits linked to your profile.\n\n"
    "Would you like me to take a look for you?"
)

EOT_18_USED = (
    "Hi [customer_name], it’s Lia from Lincoln Audi.\n\n"
    "I’ve been reviewing your account and you’re now around 18 months from the end "
    "of your Approved Used agreement.\n\n"
    "This is a useful point to check how your current plan is shaping up and start "
    "thinking about what you might want next.\n\n"
    "If there’s a particular type of car you’ve got your eye on for your next upgrade, "
    "I can start looking at options nice and early – whether that’s another Approved "
    "Used model or trying a brand new Audi, where you now qualify for exclusive "
    "loyalty contributions.\n\n"
    "Would you like me to take a look for you?"
)

EOT_18_INTRO = (
    "Thanks for getting back to me, [customer_name].\n\n"
    "You’re around 18 months from the end of your agreement now, which makes this "
    "a good time to do a quick end-of-warranty review and make sure there are no "
    "surprises coming up.\n\n"
    "I can check your agreement, mileage and profile, confirm everything is on track, "
    "and see whether there are any early upgrade options that might work in your favour – "
    "or if it’s better to simply carry on as you are for now.\n\n"
    "Would you like me to check what that looks like for you?"
)

2. Make sure there is a dictionary called LIA_EOT_CAMPAIGN_OPENERS.
- If it already exists, add two entries to it:
    "EOT_18_NEW": EOT_18_NEW,
    "EOT_18_USED": EOT_18_USED,
- If it does NOT exist yet, create it near the other LIA_* dictionaries and include those two keys.

3. Make sure there is a dictionary called LIA_EOT_INTROS.
- If it already exists, add an entry:
    "EOT_18": EOT_18_INTRO,
- If it does NOT exist yet, create it near the other LIA_* dictionaries and include:
    "EOT_18": EOT_18_INTRO

4. Do not change any existing keys or logic – just add these new constants and mappings.